Develop Reference

Increase checkbox dimension in listview c# [duplicate]

I'm using a checkbox control like this:
<CheckBox VerticalAlignment="Bottom" IsChecked="{Binding Selected}"
Grid.Column="0"
FontSize="{StaticResource PhoneFontSizeLarge}"
Content="{Binding Name}">
</CheckBox>
The thing is that I change size to be a little bigger. In this case text is getting bigger, but tick itself remains the same. It looks ugly, can I resize checkbox somehow?
UPDATE
I'm doing it on windows phone so LayoutTransform not appropriate here

Try some thing like this:-
<CheckBox>
<CheckBox.LayoutTransform>
<ScaleTransform ScaleX="2" ScaleY="2" />
</CheckBox.LayoutTransform>
</CheckBox>
You can also check this link

<StackPanel Height="80"
Name="StackPanel1"
Orientation="Horizontal">
<Viewbox Height="{Binding Path=ActualHeight, ElementName=StackPanel1}">
<CheckBox />
</Viewbox>
</StackPanel>
Adjust the StackPanel height as needed.

Ended up with the following:
Add an empty checkbox
Open control in expression blend
Select checkbox there
Open Edit Template -> Edit Copy
It will create a new style with custom template that you will be able to assign to checkboxes.
It produced about 150 loc style, but I couldn't find another way

ScaleTransform scale = new ScaleTransform(2.0, 2.0);
yourCheckBox.RenderTransformOrigin = new Point(0.5, 0.5);
yourCheckBox.RenderTransform = scale;

Just add below mention codes in windows/usercontrol resource, it will automatically increase the default size of the []checkbox inside a Xaml control.
<Style x:Key="FocusVisual">
<Setter Property="Control.Template">
<Setter.Value>
<ControlTemplate>
<Rectangle Margin="2" SnapsToDevicePixels="true" Stroke="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}" StrokeThickness="1" StrokeDashArray="1 2"/>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<SolidColorBrush x:Key="OptionMark.Static.Background" Color="#FFFFFFFF"/>
<SolidColorBrush x:Key="OptionMark.Static.Border" Color="#FF707070"/>
<Style x:Key="OptionMarkFocusVisual">
<Setter Property="Control.Template">
<Setter.Value>
<ControlTemplate>
<Rectangle Margin="14,0,0,0" SnapsToDevicePixels="true" Stroke="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}" StrokeThickness="1" StrokeDashArray="1 2"/>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<SolidColorBrush x:Key="OptionMark.MouseOver.Background" Color="#FFF3F9FF"/>
<SolidColorBrush x:Key="OptionMark.MouseOver.Border" Color="#FF5593FF"/>
<SolidColorBrush x:Key="OptionMark.MouseOver.Glyph" Color="#FF212121"/>
<SolidColorBrush x:Key="OptionMark.Disabled.Background" Color="#FFE6E6E6"/>
<SolidColorBrush x:Key="OptionMark.Disabled.Border" Color="#FFBCBCBC"/>
<SolidColorBrush x:Key="OptionMark.Disabled.Glyph" Color="#FF707070"/>
<SolidColorBrush x:Key="OptionMark.Pressed.Background" Color="#FFD9ECFF"/>
<SolidColorBrush x:Key="OptionMark.Pressed.Border" Color="#FF3C77DD"/>
<SolidColorBrush x:Key="OptionMark.Pressed.Glyph" Color="#FF212121"/>
<SolidColorBrush x:Key="OptionMark.Static.Glyph" Color="#FF212121"/>
<Style TargetType="{x:Type CheckBox}">
<Setter Property="FocusVisualStyle" Value="{StaticResource FocusVisual}"/>
<Setter Property="Background" Value="{StaticResource OptionMark.Static.Background}"/>
<Setter Property="BorderBrush" Value="{StaticResource OptionMark.Static.Border}"/>
<Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}"/>
<Setter Property="BorderThickness" Value="1"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type CheckBox}">
<Grid x:Name="templateRoot" Background="Transparent" SnapsToDevicePixels="True">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<Border x:Name="checkBoxBorder" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="1" VerticalAlignment="{TemplateBinding VerticalContentAlignment}">
<Grid x:Name="markGrid">
<Path x:Name="optionMark" Data="F1 M 9.97498,1.22334L 4.6983,9.09834L 4.52164,9.09834L 0,5.19331L 1.27664,3.52165L 4.255,6.08833L 8.33331,1.52588e-005L 9.97498,1.22334 Z "
Fill="{StaticResource OptionMark.Pressed.Glyph}" Margin="5" Opacity="0" Stretch="Uniform"/>
<Rectangle x:Name="indeterminateMark" Fill="{StaticResource OptionMark.Static.Glyph}" Margin="2" Opacity="0"/>
</Grid>
</Border>
<ContentPresenter x:Name="contentPresenter" Grid.Column="1" Focusable="False" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="{TemplateBinding Padding}" RecognizesAccessKey="True" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" VerticalAlignment="{TemplateBinding VerticalContentAlignment}"/>
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="HasContent" Value="true">
<Setter Property="FocusVisualStyle" Value="{StaticResource OptionMarkFocusVisual}"/>
<Setter Property="Padding" Value="4,-1,0,0"/>
</Trigger>
<Trigger Property="IsMouseOver" Value="true">
<Setter Property="Background" TargetName="checkBoxBorder" Value="{StaticResource OptionMark.MouseOver.Background}"/>
<Setter Property="BorderBrush" TargetName="checkBoxBorder" Value="{StaticResource OptionMark.MouseOver.Border}"/>
<Setter Property="Fill" TargetName="optionMark" Value="{StaticResource OptionMark.MouseOver.Glyph}"/>
<Setter Property="Fill" TargetName="indeterminateMark" Value="{StaticResource OptionMark.MouseOver.Glyph}"/>
</Trigger>
<Trigger Property="IsEnabled" Value="false">
<Setter Property="Background" TargetName="checkBoxBorder" Value="{StaticResource OptionMark.Disabled.Background}"/>
<Setter Property="BorderBrush" TargetName="checkBoxBorder" Value="{StaticResource OptionMark.Disabled.Border}"/>
<Setter Property="Fill" TargetName="optionMark" Value="{StaticResource OptionMark.Disabled.Glyph}"/>
<Setter Property="Fill" TargetName="indeterminateMark" Value="{StaticResource OptionMark.Disabled.Glyph}"/>
</Trigger>
<Trigger Property="IsPressed" Value="true">
<Setter Property="Background" TargetName="checkBoxBorder" Value="{StaticResource OptionMark.Pressed.Background}"/>
<Setter Property="BorderBrush" TargetName="checkBoxBorder" Value="{StaticResource OptionMark.Pressed.Border}"/>
<Setter Property="Fill" TargetName="optionMark" Value="{StaticResource OptionMark.Pressed.Glyph}"/>
<Setter Property="Fill" TargetName="indeterminateMark" Value="{StaticResource OptionMark.Pressed.Glyph}"/>
</Trigger>
<Trigger Property="IsChecked" Value="true">
<Setter Property="Opacity" TargetName="optionMark" Value="1"/>
<Setter Property="Opacity" TargetName="indeterminateMark" Value="0"/>
</Trigger>
<Trigger Property="IsChecked" Value="{x:Null}">
<Setter Property="Opacity" TargetName="optionMark" Value="0"/>
<Setter Property="Opacity" TargetName="indeterminateMark" Value="1"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>

WPF Modified example
markGrid Width="24", Height="24"
optionMark Margin="4", Stretch="Uniform"
indeterminateMark Margin="4"
<Style x:Key="FocusVisual">
<Setter Property="Control.Template">
<Setter.Value>
<ControlTemplate>
<Rectangle Margin="2" StrokeDashArray="1 2" Stroke="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}" SnapsToDevicePixels="true" StrokeThickness="1"/>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<Style x:Key="OptionMarkFocusVisual">
<Setter Property="Control.Template">
<Setter.Value>
<ControlTemplate>
<Rectangle Margin="14,0,0,0" StrokeDashArray="1 2" Stroke="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}" SnapsToDevicePixels="true" StrokeThickness="1"/>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<SolidColorBrush x:Key="OptionMark.Static.Background" Color="#FFFFFFFF"/>
<SolidColorBrush x:Key="OptionMark.Static.Border" Color="#FF707070"/>
<SolidColorBrush x:Key="OptionMark.Static.Glyph" Color="#FF212121"/>
<SolidColorBrush x:Key="OptionMark.MouseOver.Background" Color="#FFF3F9FF"/>
<SolidColorBrush x:Key="OptionMark.MouseOver.Border" Color="#FF5593FF"/>
<SolidColorBrush x:Key="OptionMark.MouseOver.Glyph" Color="#FF212121"/>
<SolidColorBrush x:Key="OptionMark.Pressed.Background" Color="#FFD9ECFF"/>
<SolidColorBrush x:Key="OptionMark.Pressed.Border" Color="#FF3C77DD"/>
<SolidColorBrush x:Key="OptionMark.Pressed.Glyph" Color="#FF212121"/>
<SolidColorBrush x:Key="OptionMark.Disabled.Background" Color="#FFE6E6E6"/>
<SolidColorBrush x:Key="OptionMark.Disabled.Border" Color="#FFBCBCBC"/>
<SolidColorBrush x:Key="OptionMark.Disabled.Glyph" Color="#FF707070"/>
<Style x:Key="CheckBoxLarge" TargetType="{x:Type CheckBox}">
<Setter Property="FocusVisualStyle" Value="{StaticResource FocusVisual}"/>
<Setter Property="Background" Value="{StaticResource OptionMark.Static.Background}"/>
<Setter Property="BorderBrush" Value="{StaticResource OptionMark.Static.Border}"/>
<Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}"/>
<Setter Property="BorderThickness" Value="1"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type CheckBox}">
<Grid x:Name="templateRoot" Background="Transparent" SnapsToDevicePixels="True">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<Border x:Name="checkBoxBorder" Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="1" VerticalAlignment="{TemplateBinding VerticalContentAlignment}">
<Grid x:Name="markGrid" Width="24" Height="24">
<!-- Width,Height,Stretch="Uniform",Margin -->
<Path x:Name="optionMark" Data="F1 M 9.97498,1.22334L 4.6983,9.09834L 4.52164,9.09834L 0,5.19331L 1.27664,3.52165L 4.255,6.08833L 8.33331,1.52588e-005L 9.97498,1.22334 Z " Fill="{StaticResource OptionMark.Static.Glyph}" Margin="4" Opacity="0" Stretch="Uniform"/>
<Rectangle x:Name="indeterminateMark" Fill="{StaticResource OptionMark.Static.Glyph}" Margin="4" Opacity="0"/>
</Grid>
</Border>
<ContentPresenter x:Name="contentPresenter" Grid.Column="1" Focusable="False" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="{TemplateBinding Padding}" RecognizesAccessKey="True" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" VerticalAlignment="{TemplateBinding VerticalContentAlignment}"/>
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="HasContent" Value="true">
<Setter Property="FocusVisualStyle" Value="{StaticResource OptionMarkFocusVisual}"/>
<Setter Property="Padding" Value="4,-1,0,0"/>
</Trigger>
<Trigger Property="IsMouseOver" Value="true">
<Setter Property="Background" TargetName="checkBoxBorder" Value="{StaticResource OptionMark.MouseOver.Background}"/>
<Setter Property="BorderBrush" TargetName="checkBoxBorder" Value="{StaticResource OptionMark.MouseOver.Border}"/>
<Setter Property="Fill" TargetName="optionMark" Value="{StaticResource OptionMark.MouseOver.Glyph}"/>
<Setter Property="Fill" TargetName="indeterminateMark" Value="{StaticResource OptionMark.MouseOver.Glyph}"/>
</Trigger>
<Trigger Property="IsEnabled" Value="false">
<Setter Property="Background" TargetName="checkBoxBorder" Value="{StaticResource OptionMark.Disabled.Background}"/>
<Setter Property="BorderBrush" TargetName="checkBoxBorder" Value="{StaticResource OptionMark.Disabled.Border}"/>
<Setter Property="Fill" TargetName="optionMark" Value="{StaticResource OptionMark.Disabled.Glyph}"/>
<Setter Property="Fill" TargetName="indeterminateMark" Value="{StaticResource OptionMark.Disabled.Glyph}"/>
</Trigger>
<Trigger Property="IsPressed" Value="true">
<Setter Property="Background" TargetName="checkBoxBorder" Value="{StaticResource OptionMark.Pressed.Background}"/>
<Setter Property="BorderBrush" TargetName="checkBoxBorder" Value="{StaticResource OptionMark.Pressed.Border}"/>
<Setter Property="Fill" TargetName="optionMark" Value="{StaticResource OptionMark.Pressed.Glyph}"/>
<Setter Property="Fill" TargetName="indeterminateMark" Value="{StaticResource OptionMark.Pressed.Glyph}"/>
</Trigger>
<Trigger Property="IsChecked" Value="true">
<Setter Property="Opacity" TargetName="optionMark" Value="1"/>
<Setter Property="Opacity" TargetName="indeterminateMark" Value="0"/>
</Trigger>
<Trigger Property="IsChecked" Value="{x:Null}">
<Setter Property="Opacity" TargetName="optionMark" Value="0"/>
<Setter Property="Opacity" TargetName="indeterminateMark" Value="1"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>

C# - Changing color of checkmark in checkbox

I have a C# application with a tick checkmark when user select the checkbox. The default color is black and not set by anyone. I would like to know the best approach to use to change the color of the checkmark, say to red instead of black.
I can't seem to find which part of the code is responsible for the color change. Tried finding resources online but it requires writing over hundred of lines of XAML just to set the color.
Any suggestion please.
EDIT:
<Setter.Value>
<ControlTemplate TargetType="{x:Type CheckBox}">
<Grid x:Name="templateRoot" Background="Transparent" SnapsToDevicePixels="True">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<Border x:Name="checkBoxBorder" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="1" VerticalAlignment="{TemplateBinding VerticalContentAlignment}">
<Grid x:Name="markGrid">
<Path x:Name="optionMark" Data="F1 M 9.97498,1.22334L 4.6983,9.09834L 4.52164,9.09834L 0,5.19331L 1.27664,3.52165L 4.255,6.08833L 8.33331,1.52588e-005L 9.97498,1.22334 Z " Fill="{StaticResource OptionMark.Static.Glyph}" Margin="1" Opacity="0" Stretch="None"/>
<Rectangle x:Name="indeterminateMark" Fill="{StaticResource OptionMark.Static.Glyph}" Margin="2" Opacity="0"/>
</Grid>
</Border>
<ContentPresenter x:Name="contentPresenter" Grid.Column="1" Focusable="False" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="{TemplateBinding Padding}" RecognizesAccessKey="True" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" VerticalAlignment="{TemplateBinding VerticalContentAlignment}"/>
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="HasContent" Value="true">
<Setter Property="FocusVisualStyle" Value="{StaticResource OptionMarkFocusVisual}"/>
<Setter Property="Padding" Value="4,-1,0,0"/>
</Trigger>
<Trigger Property="IsMouseOver" Value="false">
<Setter Property="Background" TargetName="checkBoxBorder" Value="{StaticResource OptionMark.MouseOver.Background}"/>
<Setter Property="BorderBrush" TargetName="checkBoxBorder" Value="{StaticResource OptionMark.MouseOver.Border}"/>
<Setter Property="Fill" TargetName="optionMark" Value="{StaticResource OptionMark.MouseOver.Glyph}"/>
<Setter Property="Fill" TargetName="indeterminateMark" Value="{StaticResource OptionMark.MouseOver.Glyph}"/>
</Trigger>
<Trigger Property="IsEnabled" Value="false">
<Setter Property="Background" TargetName="checkBoxBorder" Value="{StaticResource OptionMark.Disabled.Background}"/>
<Setter Property="BorderBrush" TargetName="checkBoxBorder" Value="{StaticResource OptionMark.Disabled.Border}"/>
<Setter Property="Fill" TargetName="optionMark" Value="{StaticResource OptionMark.Disabled.Glyph}"/>
<Setter Property="Fill" TargetName="indeterminateMark" Value="{StaticResource OptionMark.Disabled.Glyph}"/>
</Trigger>
<Trigger Property="IsChecked" Value="true">
<Setter Property="Opacity" TargetName="optionMark" Value="1" />
<Setter Property="Opacity" TargetName="indeterminateMark" Value="0"/>
</Trigger>
<Trigger Property="IsChecked" Value="{x:Null}" >
<Setter Property="Opacity" TargetName="optionMark" Value="0"/>
<Setter Property="Opacity" TargetName="indeterminateMark" Value="1"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>

I understand that you want to avoid writing over hundered of lines of XAML just to set the color, but from Visual Studio 2012 onwards, there's a feature where you can edit a copy of the control template. In Design mode, right click on the checkbox control, select Edit Template > Edit A Copy...
Then you can set where to define the template at, so you could either reuse it or just use it for one checkbox.
These are the colors you need to manipulate if you're on Windows 8 or above since the template varies base on Windows version. (The generated template has the following code)
<CheckBox.Resources>
<Style x:Key="FocusVisual">
<Setter Property="Control.Template">
<Setter.Value>
<ControlTemplate>
<Rectangle Margin="2" SnapsToDevicePixels="true" Stroke="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}" StrokeThickness="1" StrokeDashArray="1 2"/>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<SolidColorBrush x:Key="OptionMark.Static.Background" Color="#FFFFFFFF"/>
<SolidColorBrush x:Key="OptionMark.Static.Border" Color="#FF707070"/>
<Style x:Key="OptionMarkFocusVisual">
<Setter Property="Control.Template">
<Setter.Value>
<ControlTemplate>
<Rectangle Margin="14,0,0,0" SnapsToDevicePixels="true" Stroke="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}" StrokeThickness="1" StrokeDashArray="1 2"/>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<SolidColorBrush x:Key="OptionMark.MouseOver.Background" Color="#FFF3F9FF"/>
<SolidColorBrush x:Key="OptionMark.MouseOver.Border" Color="#FF5593FF"/>
<SolidColorBrush x:Key="OptionMark.MouseOver.Glyph" Color="#FF212121"/>
<SolidColorBrush x:Key="OptionMark.Disabled.Background" Color="#FFE6E6E6"/>
<SolidColorBrush x:Key="OptionMark.Disabled.Border" Color="#FFBCBCBC"/>
<SolidColorBrush x:Key="OptionMark.Disabled.Glyph" Color="#FF707070"/>
<SolidColorBrush x:Key="OptionMark.Pressed.Background" Color="#FFD9ECFF"/>
<SolidColorBrush x:Key="OptionMark.Pressed.Border" Color="#FF3C77DD"/>
<SolidColorBrush x:Key="OptionMark.Pressed.Glyph" Color="#FF212121"/>
<SolidColorBrush x:Key="OptionMark.Static.Glyph" Color="#FF212121"/>
<Style x:Key="CheckBoxStyleCustom" TargetType="{x:Type CheckBox}">
<Setter Property="FocusVisualStyle" Value="{StaticResource FocusVisual}"/>
<Setter Property="Background" Value="{StaticResource OptionMark.Static.Background}"/>
<Setter Property="BorderBrush" Value="{StaticResource OptionMark.Static.Border}"/>
<Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}"/>
<Setter Property="BorderThickness" Value="1"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type CheckBox}">
<Grid x:Name="templateRoot" Background="Transparent" SnapsToDevicePixels="True">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<Border x:Name="checkBoxBorder" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="1" VerticalAlignment="{TemplateBinding VerticalContentAlignment}">
<Grid x:Name="markGrid">
<Path x:Name="optionMark" Data="F1 M 9.97498,1.22334L 4.6983,9.09834L 4.52164,9.09834L 0,5.19331L 1.27664,3.52165L 4.255,6.08833L 8.33331,1.52588e-005L 9.97498,1.22334 Z " Fill="{StaticResource OptionMark.Static.Glyph}" Margin="1" Opacity="0" Stretch="None"/>
<Rectangle x:Name="indeterminateMark" Fill="{StaticResource OptionMark.Static.Glyph}" Margin="2" Opacity="0"/>
</Grid>
</Border>
<ContentPresenter x:Name="contentPresenter" Grid.Column="1" Focusable="False" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="{TemplateBinding Padding}" RecognizesAccessKey="True" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" VerticalAlignment="{TemplateBinding VerticalContentAlignment}"/>
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="HasContent" Value="true">
<Setter Property="FocusVisualStyle" Value="{StaticResource OptionMarkFocusVisual}"/>
<Setter Property="Padding" Value="4,-1,0,0"/>
</Trigger>
<Trigger Property="IsMouseOver" Value="true">
<Setter Property="Background" TargetName="checkBoxBorder" Value="{StaticResource OptionMark.MouseOver.Background}"/>
<Setter Property="BorderBrush" TargetName="checkBoxBorder" Value="{StaticResource OptionMark.MouseOver.Border}"/>
<Setter Property="Fill" TargetName="optionMark" Value="{StaticResource OptionMark.MouseOver.Glyph}"/>
<Setter Property="Fill" TargetName="indeterminateMark" Value="{StaticResource OptionMark.MouseOver.Glyph}"/>
</Trigger>
<Trigger Property="IsEnabled" Value="false">
<Setter Property="Background" TargetName="checkBoxBorder" Value="{StaticResource OptionMark.Disabled.Background}"/>
<Setter Property="BorderBrush" TargetName="checkBoxBorder" Value="{StaticResource OptionMark.Disabled.Border}"/>
<Setter Property="Fill" TargetName="optionMark" Value="{StaticResource OptionMark.Disabled.Glyph}"/>
<Setter Property="Fill" TargetName="indeterminateMark" Value="{StaticResource OptionMark.Disabled.Glyph}"/>
</Trigger>
<Trigger Property="IsPressed" Value="true">
<Setter Property="Background" TargetName="checkBoxBorder" Value="{StaticResource OptionMark.Pressed.Background}"/>
<Setter Property="BorderBrush" TargetName="checkBoxBorder" Value="{StaticResource OptionMark.Pressed.Border}"/>
<Setter Property="Fill" TargetName="optionMark" Value="{StaticResource OptionMark.Pressed.Glyph}"/>
<Setter Property="Fill" TargetName="indeterminateMark" Value="{StaticResource OptionMark.Pressed.Glyph}"/>
</Trigger>
<Trigger Property="IsChecked" Value="true">
<Setter Property="Opacity" TargetName="optionMark" Value="1"/>
<Setter Property="Opacity" TargetName="indeterminateMark" Value="0"/>
</Trigger>
<Trigger Property="IsChecked" Value="{x:Null}">
<Setter Property="Opacity" TargetName="optionMark" Value="0"/>
<Setter Property="Opacity" TargetName="indeterminateMark" Value="1"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</CheckBox.Resources>
Edit: The ones that you have to modify to change the Check symbol colors are:
<SolidColorBrush x:Key="OptionMark.MouseOver.Glyph" Color="#FF212121"/>
<SolidColorBrush x:Key="OptionMark.Disabled.Glyph" Color="#FF707070"/>
<SolidColorBrush x:Key="OptionMark.Pressed.Glyph" Color="#FF212121"/>
<SolidColorBrush x:Key="OptionMark.Static.Glyph" Color="#FF212121"/>

For anyone who needs a simple CheckBox Template
<Style x:Key="CheckBoxStyle" TargetType="CheckBox">
<Setter Property="HorizontalAlignment" Value="Center"/>
<Setter Property="VerticalAlignment" Value="Center"/>
<Setter Property="Background" Value="Green"/>
<Setter Property="Foreground" Value="Transparent"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate>
<Border BorderBrush="White" BorderThickness="1">
<Grid Width="15" Height="15" >
<Rectangle Fill="{TemplateBinding Background}"/>
<TextBlock Foreground="{TemplateBinding Foreground}" Margin="0 0 0 1" VerticalAlignment="Center" HorizontalAlignment="Center" Text="√"/>
</Grid>
</Border>
</ControlTemplate>
</Setter.Value>
</Setter>
<Style.Triggers>
<Trigger Property="IsChecked" Value="True">
<Setter Property="Foreground" Value="White"/>
</Trigger>
<Trigger Property="IsMouseOver" Value="True">
<Setter Property="Background" Value="Red"/>
</Trigger>
</Style.Triggers>
</Style>

Checkbox with RightToLeft flow direction in Windows 8.1

Why checkbox checked mark appears with mirrored image in windows 8.1, when applying FlowDirection as RightToLeft. it is normally in other windows os.
<CheckBox HorizontalAlignment="Center" VerticalAlignment="Center" IsChecked="True"
FlowDirection="RightToLeft">

I found this answer on another search..
You could set your own style to the checkbox:
<Window x:Class="WpfApplication21.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525">
<Window.Resources>
<Style x:Key="CheckBoxStyle1" TargetType="{x:Type CheckBox}">
<Setter Property="FocusVisualStyle">
<Setter.Value>
<Style>
<Setter Property="Control.Template">
<Setter.Value>
<ControlTemplate>
<Rectangle Margin="2" SnapsToDevicePixels="True" Stroke="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}" StrokeThickness="1" StrokeDashArray="1 2"/>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Setter.Value>
</Setter>
<Setter Property="Background" Value="White"/>
<Setter Property="BorderBrush" Value="#FF707070"/>
<Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}"/>
<Setter Property="BorderThickness" Value="1"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type CheckBox}">
<Grid x:Name="templateRoot" Background="Transparent" SnapsToDevicePixels="True">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<Border x:Name="checkBoxBorder" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="1" VerticalAlignment="{TemplateBinding VerticalContentAlignment}">
<Grid x:Name="markGrid">
<Path FlowDirection="LeftToRight" x:Name="optionMark" Data="F1M9.97498,1.22334L4.6983,9.09834 4.52164,9.09834 0,5.19331 1.27664,3.52165 4.255,6.08833 8.33331,1.52588E-05 9.97498,1.22334z" Fill="#FF212121" Margin="1" Opacity="0" Stretch="None"/>
<Rectangle x:Name="indeterminateMark" Fill="#FF212121" Margin="2" Opacity="0"/>
</Grid>
</Border>
<ContentPresenter x:Name="contentPresenter" ContentTemplate="{TemplateBinding ContentTemplate}" Content="{TemplateBinding Content}" Grid.Column="1" ContentStringFormat="{TemplateBinding ContentStringFormat}" Focusable="False" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="{TemplateBinding Padding}" RecognizesAccessKey="True" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" VerticalAlignment="{TemplateBinding VerticalContentAlignment}"/>
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="HasContent" Value="True">
<Setter Property="FocusVisualStyle">
<Setter.Value>
<Style>
<Setter Property="Control.Template">
<Setter.Value>
<ControlTemplate>
<Rectangle Margin="14,0,0,0" SnapsToDevicePixels="True" Stroke="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}" StrokeThickness="1" StrokeDashArray="1 2"/>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Setter.Value>
</Setter>
<Setter Property="Padding" Value="4,-1,0,0"/>
</Trigger>
<Trigger Property="IsMouseOver" Value="True">
<Setter Property="Background" TargetName="checkBoxBorder" Value="#FFF3F9FF"/>
<Setter Property="BorderBrush" TargetName="checkBoxBorder" Value="#FF5593FF"/>
<Setter Property="Fill" TargetName="optionMark" Value="#FF212121"/>
<Setter Property="Fill" TargetName="indeterminateMark" Value="#FF212121"/>
</Trigger>
<Trigger Property="IsEnabled" Value="False">
<Setter Property="Background" TargetName="checkBoxBorder" Value="#FFE6E6E6"/>
<Setter Property="BorderBrush" TargetName="checkBoxBorder" Value="#FFBCBCBC"/>
<Setter Property="Fill" TargetName="optionMark" Value="#FF707070"/>
<Setter Property="Fill" TargetName="indeterminateMark" Value="#FF707070"/>
</Trigger>
<Trigger Property="IsPressed" Value="True">
<Setter Property="Background" TargetName="checkBoxBorder" Value="#FFD9ECFF"/>
<Setter Property="BorderBrush" TargetName="checkBoxBorder" Value="#FF3C77DD"/>
<Setter Property="Fill" TargetName="optionMark" Value="#FF212121"/>
<Setter Property="Fill" TargetName="indeterminateMark" Value="#FF212121"/>
</Trigger>
<Trigger Property="IsChecked" Value="True">
<Setter Property="Opacity" TargetName="optionMark" Value="1"/>
<Setter Property="Opacity" TargetName="indeterminateMark" Value="0"/>
</Trigger>
<Trigger Property="IsChecked" Value="{x:Null}">
<Setter Property="Opacity" TargetName="optionMark" Value="0"/>
<Setter Property="Opacity" TargetName="indeterminateMark" Value="1"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Window.Resources>
<Grid>
<CheckBox HorizontalAlignment="Center" VerticalAlignment="Center" IsChecked="True"
FlowDirection="RightToLeft" Content="CheckBox" Style="{DynamicResource CheckBoxStyle1}"/>
</Grid>
</Window>
Although the look will be slightly different but you can either go with it or change the style as well.

if you want this as same in other OS, edit the template and hard code as left to right for the Tick.

combobox IsFocused problems wpf

I've created wpf ComboBox template. And I've added trigger on IsFocused property, to change my ComboBox Border color. But for some reasons it's working only when It's focused with Tab button. It doesn't change border color when I made selection in Combobox. How to solve this problem? Here is template code:
<Style x:Key="ComboBoxFocusVisual">
<Setter Property="Control.Template">
<Setter.Value>
<ControlTemplate>
<Border BorderBrush="#FF1388B7" BorderThickness="2,2,2,2" CornerRadius="3"></Border>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<Geometry x:Key="DownArrowGeometry">M 0 0 L 3.5 4 L 7 0 Z</Geometry>
<Style x:Key="ComboBoxReadonlyToggleButton" TargetType="{x:Type ToggleButton}">
<Setter Property="OverridesDefaultStyle" Value="true"/>
<Setter Property="IsTabStop" Value="false"/>
<Setter Property="FocusVisualStyle" Value="{StaticResource ComboBoxFocusVisual}"/>
<Setter Property="Focusable" Value="True"/>
<Setter Property="ClickMode" Value="Press"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ToggleButton}">
<Border x:Name="Chrome" SnapsToDevicePixels="true" BorderBrush="#c1bebe" BorderThickness="2,2,2,2" CornerRadius="3,3,3,3">
<Border.Background>
<LinearGradientBrush>
<GradientStop Color="#fffae5" Offset="1"/>
</LinearGradientBrush>
</Border.Background>
<Grid HorizontalAlignment="Right" Width="20">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="3"/>
<ColumnDefinition/>
</Grid.ColumnDefinitions>
<Path Grid.Column="1" Fill="#FF436B13" HorizontalAlignment="Center" Margin="3,1,0,0" x:Name="Arrow" VerticalAlignment="Center" Data="{StaticResource DownArrowGeometry}"/>
</Grid>
</Border>
<ControlTemplate.Triggers>
<Trigger Property="IsChecked" Value="True">
<Setter Property="BorderThickness" TargetName="Chrome" Value="2,2,2,0.5"/>
<Setter Property="CornerRadius" TargetName="Chrome" Value="3,3,2,2"/>
<Setter Property="BorderBrush" TargetName="Chrome" Value="#FF1388B7"/>
<Setter Property="Background" TargetName="Chrome" Value="#fef2be"/>
</Trigger>
<Trigger Property="IsFocused" Value="True">
<Setter Property="BorderBrush" Value="#FF1388B7" TargetName="Chrome"/>
</Trigger>
<Trigger Property="IsEnabled" Value="False">
<Setter Property="Background" TargetName="Chrome" Value="LightGray"></Setter>
</Trigger>
<Trigger Property="IsMouseOver" Value="true">
<Setter TargetName="Chrome" Property="BorderBrush" Value="#83bff6" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<LinearGradientBrush x:Key="TextBoxBorder" MappingMode="Absolute" EndPoint="0,20" StartPoint="0,0">
<GradientStop Color="Red" Offset="1"/>
</LinearGradientBrush>
<Style x:Key="ComboBoxEditableTextBox" TargetType="{x:Type TextBox}">
<Setter Property="OverridesDefaultStyle" Value="true"/>
<Setter Property="AllowDrop" Value="true"/>
<Setter Property="MinWidth" Value="0"/>
<Setter Property="MinHeight" Value="0"/>
<Setter Property="FocusVisualStyle" Value="{x:Null}"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type TextBox}">
<ScrollViewer x:Name="PART_ContentHost" Background="Transparent" Focusable="False" HorizontalScrollBarVisibility="Hidden" VerticalScrollBarVisibility="Auto"/>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<Style x:Key="ComboBoxToggleButton" TargetType="{x:Type ToggleButton}">
<Setter Property="OverridesDefaultStyle" Value="true"/>
<Setter Property="FocusVisualStyle" Value="{StaticResource ComboBoxFocusVisual}"/>
<Setter Property="IsTabStop" Value="True"/>
<Setter Property="Focusable" Value="True"/>
<Setter Property="ClickMode" Value="Press"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ToggleButton}">
<Microsoft_Windows_Themes:ButtonChrome x:Name="Chrome" Width="{DynamicResource {x:Static SystemParameters.VerticalScrollBarWidthKey}}" SnapsToDevicePixels="true" Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" RenderMouseOver="{TemplateBinding IsMouseOver}" RenderPressed="{TemplateBinding IsPressed}" RoundCorners="false">
<Path Fill="Black" HorizontalAlignment="Center" Margin="0,1,0,0" x:Name="Arrow" VerticalAlignment="Center" Data="{StaticResource DownArrowGeometry}"/>
</Microsoft_Windows_Themes:ButtonChrome>
<ControlTemplate.Triggers>
<Trigger Property="IsChecked" Value="true">
<Setter Property="RenderPressed" TargetName="Chrome" Value="true"/>
</Trigger>
<Trigger Property="IsEnabled" Value="false">
<Setter Property="Fill" TargetName="Arrow" Value="#AFAFAF"/>
</Trigger>
<Trigger Property="IsFocused" Value="True">
<Setter Property="BorderBrush" Value="#FF1388B7" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<ControlTemplate x:Key="ComboBoxEditableTemplate" TargetType="{x:Type ComboBox}">
<Grid x:Name="Placement" SnapsToDevicePixels="true">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*"/>
<ColumnDefinition Width="Auto"/>
</Grid.ColumnDefinitions>
<Popup x:Name="PART_Popup" AllowsTransparency="true" IsOpen="{Binding Path=IsDropDownOpen, RelativeSource={RelativeSource TemplatedParent}}" Placement="Bottom" PopupAnimation="{DynamicResource {x:Static SystemParameters.ComboBoxPopupAnimationKey}}" Grid.ColumnSpan="2">
</Popup>
<Microsoft_Windows_Themes:ListBoxChrome x:Name="Border" Grid.ColumnSpan="2" Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" RenderFocused="{TemplateBinding IsKeyboardFocusWithin}" RenderMouseOver="{TemplateBinding IsMouseOver}"/>
<TextBox Margin="{TemplateBinding Padding}" x:Name="PART_EditableTextBox" Style="{StaticResource ComboBoxEditableTextBox}" HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}" VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}" IsReadOnly="{Binding Path=IsReadOnly, RelativeSource={RelativeSource TemplatedParent}}"/>
<ToggleButton Style="{StaticResource ComboBoxToggleButton}" Grid.Column="1" IsChecked="{Binding Path=IsDropDownOpen, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}"/>
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="IsKeyboardFocusWithin" Value="true">
<Setter Property="Foreground" Value="Black"/>
</Trigger>
<Trigger Property="IsDropDownOpen" Value="true">
<Setter Property="RenderFocused" TargetName="Border" Value="true"/>
</Trigger>
<Trigger Property="IsGrouping" Value="true">
<Setter Property="ScrollViewer.CanContentScroll" Value="false"/>
</Trigger>
<Trigger Property="IsFocused" Value="True">
<Setter Property="BorderBrush" Value="#FF1388B7" TargetName="Border"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
<Style TargetType="{x:Type ComboBox}">
<Setter Property="FocusVisualStyle" Value="{StaticResource ComboBoxFocusVisual}"/>
<Setter Property="Foreground" Value="Black"/>
<Setter Property="HorizontalContentAlignment" Value="Left"></Setter>
<Setter Property="VerticalContentAlignment" Value="Center"/>
<Setter Property="ScrollViewer.HorizontalScrollBarVisibility" Value="Auto"/>
<Setter Property="ScrollViewer.VerticalScrollBarVisibility" Value="Auto"/>
<Setter Property="Padding" Value="4,3"/>
<Setter Property="Margin" Value="5"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ComboBox}">
<Grid x:Name="MainGrid" SnapsToDevicePixels="true">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*"/>
<ColumnDefinition MinWidth="{DynamicResource {x:Static SystemParameters.VerticalScrollBarWidthKey}}" Width="0"/>
</Grid.ColumnDefinitions>
<Popup Margin="1" x:Name="PART_Popup" AllowsTransparency="true" IsOpen="{Binding Path=IsDropDownOpen, RelativeSource={RelativeSource TemplatedParent}}" Placement="Bottom" PopupAnimation="{DynamicResource {x:Static SystemParameters.ComboBoxPopupAnimationKey}}" Grid.ColumnSpan="2">
<Border x:Name="DropDownBorder" Background="#f6fafe" MaxHeight="{TemplateBinding MaxDropDownHeight}" MinWidth="{Binding Path=ActualWidth, ElementName=MainGrid}" BorderBrush="#FF1388B7" BorderThickness="2,0,2,2" CornerRadius="0,0,4,4">
<ScrollViewer CanContentScroll="true">
<ItemsPresenter SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" KeyboardNavigation.DirectionalNavigation="Contained"/>
</ScrollViewer>
</Border>
</Popup>
<ToggleButton Style="{StaticResource ComboBoxReadonlyToggleButton}" Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" Grid.ColumnSpan="2" IsChecked="{Binding Path=IsDropDownOpen, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}"/>
<ContentPresenter HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="{TemplateBinding Padding}" VerticalAlignment="{TemplateBinding VerticalContentAlignment}" IsHitTestVisible="false" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" Content="{TemplateBinding SelectionBoxItem}" ContentTemplate="{TemplateBinding SelectionBoxItemTemplate}" ContentTemplateSelector="{TemplateBinding ItemTemplateSelector}"/>
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="HasItems" Value="false">
<Setter Property="Height" TargetName="DropDownBorder" Value="90"/>
</Trigger>
<Trigger Property="IsEnabled" Value="false">
<Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
<Setter Property="Background" Value="#FFF4F4F4"/>
</Trigger>
<Trigger Property="IsFocused" Value="True">
<Setter Property="BorderBrush" Value="#FF1388B7"/>
</Trigger>
<Trigger Property="IsGrouping" Value="true">
<Setter Property="ScrollViewer.CanContentScroll" Value="false"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
<Setter Property="FontFamily" Value="Tahoma"/>
<Setter Property="FontSize" Value="12"/>
<Style.Triggers>
<Trigger Property="IsEditable" Value="true">
<Setter Property="BorderBrush" Value="{StaticResource TextBoxBorder}"/>
<Setter Property="Background" Value="{DynamicResource {x:Static SystemColors.WindowBrushKey}}"/>
<Setter Property="IsTabStop" Value="false"/>
<Setter Property="Padding" Value="3"/>
<Setter Property="Template" Value="{StaticResource ComboBoxEditableTemplate}"/>
</Trigger>
</Style.Triggers>
</Style>
<Style TargetType="{x:Type ComboBoxItem}">
<Setter Property="HorizontalContentAlignment" Value="{Binding Path=HorizontalContentAlignment, RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}"/>
<Setter Property="VerticalContentAlignment" Value="{Binding Path=VerticalContentAlignment, RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}"/>
<Setter Property="Padding" Value="3,0,3,0"/>
<Setter Property="Background" Value="Transparent"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ComboBoxItem}">
<Border x:Name="Bd" SnapsToDevicePixels="true" Background="{TemplateBinding Background}" Padding="{TemplateBinding Padding}" Margin="2,2,2,2">
<ContentPresenter HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" VerticalAlignment="{TemplateBinding VerticalContentAlignment}" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
</Border>
<ControlTemplate.Triggers>
<Trigger Property="IsHighlighted" Value="true">
<Setter Property="Background" TargetName="Bd" Value="{DynamicResource {x:Static SystemColors.HighlightBrushKey}}"/>
<Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.HighlightTextBrushKey}}"/>
</Trigger>
<Trigger Property="IsEnabled" Value="false">
<Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>

The problem appears to be with WPF's DependencyProperty Precedence rules
The color specified in ComboBoxReadonlyToggleButton Style:
<Border x:Name="Chrome" SnapsToDevicePixels="true" BorderBrush="#c1bebe"
BorderThickness="2,2,2,2" CornerRadius="3,3,3,3">
is taking precendence over the triggered color defined in your ComboBox's ControlTemplate.Triggers
<Trigger Property="IsFocused" Value="True">
<Setter Property="BorderBrush" Value="#FF1388B7"/>
</Trigger>
Change it to {TemplateBinding BorderBrush} and it will work correctly
<Border x:Name="Chrome" SnapsToDevicePixels="true"
BorderBrush="{TemplateBinding BorderBrush}"
BorderThickness="2,2,2,2" CornerRadius="3,3,3,3">

How can I make a WPF Expander Stretch?

The Expander control in WPF does not stretch to fill all the available space. Is there any solutions in XAML for this?

All you need to do is this:
<Expander>
<Expander.Header>
<TextBlock
Text="I am header text..."
Background="Blue"
Width="{Binding
RelativeSource={RelativeSource
Mode=FindAncestor,
AncestorType={x:Type Expander}},
Path=ActualWidth}"
/>
</Expander.Header>
<TextBlock Background="Red">
I am some content...
</TextBlock>
</Expander>
http://joshsmithonwpf.wordpress.com/2007/02/24/stretching-content-in-an-expander-header/

Non stretchable Expanders is usually the problem of non stretchable parent controls.. Perhaps one of the parent controls has defined a HorizontalAlignment or VerticalAlignment property?
If you can post some sample code, we can give you a better answer.

This solution is a lot simpler and does not effect other expander controls you may using in your application.
<Expander ExpandDirection="Right" Grid.Column="0" Name="topOfB">
<Expander.Header>
<Grid HorizontalAlignment="Stretch" Width="{Binding Path=ActualWidth, ElementName=topOfB}">
<!-- control content goes here -->

The accepted answer draws outside the control because the header content is in one column and the expander button is in the first. Might be good enough for some cases.
If you want a clean solution you have to change the template of the expander.
Another way is an attached property:
using System.Collections.Generic;
using System.Linq;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;
public static class ParentContentPresenter
{
public static readonly System.Windows.DependencyProperty HorizontalAlignmentProperty = System.Windows.DependencyProperty.RegisterAttached(
"HorizontalAlignment",
typeof(HorizontalAlignment),
typeof(ParentContentPresenter),
new PropertyMetadata(default(HorizontalAlignment), OnHorizontalAlignmentChanged));
public static void SetHorizontalAlignment(this UIElement element, HorizontalAlignment value)
{
element.SetValue(HorizontalAlignmentProperty, value);
}
[AttachedPropertyBrowsableForChildren(IncludeDescendants = false)]
[AttachedPropertyBrowsableForType(typeof(UIElement))]
public static HorizontalAlignment GetHorizontalAlignment(this UIElement element)
{
return (HorizontalAlignment)element.GetValue(HorizontalAlignmentProperty);
}
private static void OnHorizontalAlignmentChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var presenter = d.Parents().OfType<ContentPresenter>().FirstOrDefault();
if (presenter != null)
{
presenter.HorizontalAlignment = (HorizontalAlignment) e.NewValue;
}
}
private static IEnumerable<DependencyObject> Parents(this DependencyObject child)
{
var parent = VisualTreeHelper.GetParent(child);
while (parent != null)
{
yield return parent;
child = parent;
parent = VisualTreeHelper.GetParent(child);
}
}
}
It lets you do:
<Expander Header="{Binding ...}">
<Expander.HeaderTemplate>
<DataTemplate>
<!--Using a border here to show how width changes-->
<Border BorderBrush="Red" BorderThickness="1"
local:ParentContentPresenter.HorizontalAlignment="Stretch">
...
</Border>
</DataTemplate>
</Expander.HeaderTemplate>
</Expander>
Note that the use of the attached property is somewhat fragile as it assumes that there is a ContentPresenter in the template.

I am pretty surprised nobody has mentioned to just edit the control template, all the other solutions have some pretty serious drawbacks weather its not calculating width properly, not redrawing, render time etc...
This control template will modify the header's contentpresenter horizontal alignment to match the actual expanders (meaning it will stretch)
<ControlTemplate x:Key="ExpanderControlTemplate1" TargetType="{x:Type Expander}">
<Border BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" CornerRadius="3" SnapsToDevicePixels="True">
<DockPanel>
<ToggleButton x:Name="HeaderSite" ContentTemplate="{TemplateBinding HeaderTemplate}" Content="{TemplateBinding Header}" DockPanel.Dock="Top" Foreground="{TemplateBinding Foreground}" FontWeight="{TemplateBinding FontWeight}" FontStyle="{TemplateBinding FontStyle}" FontStretch="{TemplateBinding FontStretch}" FontSize="{TemplateBinding FontSize}" FontFamily="{TemplateBinding FontFamily}" HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}" IsChecked="{Binding IsExpanded, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}" Margin="1" MinWidth="0" MinHeight="0" Padding="{TemplateBinding Padding}" VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}">
<ToggleButton.FocusVisualStyle>
<Style>
<Setter Property="Control.Template">
<Setter.Value>
<ControlTemplate>
<Border>
<Rectangle Margin="0" SnapsToDevicePixels="True" Stroke="Black" StrokeThickness="1" StrokeDashArray="1 2"/>
</Border>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</ToggleButton.FocusVisualStyle>
<ToggleButton.Style>
<Style TargetType="{x:Type ToggleButton}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ToggleButton}">
<Border Padding="{TemplateBinding Padding}">
<Grid Background="Transparent" SnapsToDevicePixels="False">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="19"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<Ellipse x:Name="circle" Fill="White" HorizontalAlignment="Center" Height="19" Stroke="#FF333333" VerticalAlignment="Center" Width="19"/>
<Path x:Name="arrow" Data="M1,1.5L4.5,5 8,1.5" HorizontalAlignment="Center" SnapsToDevicePixels="False" Stroke="#FF333333" StrokeThickness="2" VerticalAlignment="Center"/>
<ContentPresenter ContentTemplate="{TemplateBinding ContentTemplate}" Content="{TemplateBinding Content}" Grid.Column="1" ContentStringFormat="{TemplateBinding ContentStringFormat}" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="4,0,0,0" RecognizesAccessKey="True" SnapsToDevicePixels="True" VerticalAlignment="Center"/>
</Grid>
</Border>
<ControlTemplate.Triggers>
<Trigger Property="IsChecked" Value="True">
<Setter Property="Data" TargetName="arrow" Value="M1,4.5L4.5,1 8,4.5"/>
</Trigger>
<Trigger Property="IsMouseOver" Value="True">
<Setter Property="Stroke" TargetName="circle" Value="#FF5593FF"/>
<Setter Property="Fill" TargetName="circle" Value="#FFF3F9FF"/>
<Setter Property="Stroke" TargetName="arrow" Value="Black"/>
</Trigger>
<Trigger Property="IsPressed" Value="True">
<Setter Property="Stroke" TargetName="circle" Value="#FF3C77DD"/>
<Setter Property="StrokeThickness" TargetName="circle" Value="1.5"/>
<Setter Property="Fill" TargetName="circle" Value="#FFD9ECFF"/>
<Setter Property="Stroke" TargetName="arrow" Value="Black"/>
</Trigger>
<Trigger Property="IsEnabled" Value="False">
<Setter Property="Stroke" TargetName="circle" Value="#FFBCBCBC"/>
<Setter Property="Fill" TargetName="circle" Value="#FFE6E6E6"/>
<Setter Property="Stroke" TargetName="arrow" Value="#FF707070"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</ToggleButton.Style>
</ToggleButton>
<ContentPresenter x:Name="ExpandSite" ContentTemplate="{TemplateBinding ContentTemplate}" Content="{TemplateBinding Content}" ContentStringFormat="{TemplateBinding ContentStringFormat}" DockPanel.Dock="Bottom" Focusable="False" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="{TemplateBinding Padding}" Visibility="Collapsed" VerticalAlignment="{TemplateBinding VerticalContentAlignment}"/>
</DockPanel>
</Border>
<ControlTemplate.Triggers>
<Trigger Property="IsExpanded" Value="True">
<Setter Property="Visibility" TargetName="ExpandSite" Value="Visible"/>
</Trigger>
<Trigger Property="ExpandDirection" Value="Right">
<Setter Property="DockPanel.Dock" TargetName="ExpandSite" Value="Right"/>
<Setter Property="DockPanel.Dock" TargetName="HeaderSite" Value="Left"/>
<Setter Property="Style" TargetName="HeaderSite">
<Setter.Value>
<Style TargetType="{x:Type ToggleButton}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ToggleButton}">
<Border Padding="{TemplateBinding Padding}">
<Grid Background="Transparent" SnapsToDevicePixels="False">
<Grid.RowDefinitions>
<RowDefinition Height="19"/>
<RowDefinition Height="*"/>
</Grid.RowDefinitions>
<Grid>
<Grid.LayoutTransform>
<TransformGroup>
<RotateTransform Angle="-90"/>
</TransformGroup>
</Grid.LayoutTransform>
<Ellipse x:Name="circle" Fill="White" HorizontalAlignment="Center" Height="19" Stroke="#FF333333" VerticalAlignment="Center" Width="19"/>
<Path x:Name="arrow" Data="M1,1.5L4.5,5 8,1.5" HorizontalAlignment="Center" SnapsToDevicePixels="False" Stroke="#FF333333" StrokeThickness="2" VerticalAlignment="Center"/>
</Grid>
<ContentPresenter ContentTemplate="{TemplateBinding ContentTemplate}" Content="{TemplateBinding Content}" ContentStringFormat="{TemplateBinding ContentStringFormat}" HorizontalAlignment="Center" Margin="0,4,0,0" Grid.Row="1" RecognizesAccessKey="True" SnapsToDevicePixels="True" VerticalAlignment="Top"/>
</Grid>
</Border>
<ControlTemplate.Triggers>
<Trigger Property="IsChecked" Value="True">
<Setter Property="Data" TargetName="arrow" Value="M1,4.5L4.5,1 8,4.5"/>
</Trigger>
<Trigger Property="IsMouseOver" Value="True">
<Setter Property="Stroke" TargetName="circle" Value="#FF5593FF"/>
<Setter Property="Fill" TargetName="circle" Value="#FFF3F9FF"/>
<Setter Property="Stroke" TargetName="arrow" Value="Black"/>
</Trigger>
<Trigger Property="IsPressed" Value="True">
<Setter Property="Stroke" TargetName="circle" Value="#FF3C77DD"/>
<Setter Property="StrokeThickness" TargetName="circle" Value="1.5"/>
<Setter Property="Fill" TargetName="circle" Value="#FFD9ECFF"/>
<Setter Property="Stroke" TargetName="arrow" Value="Black"/>
</Trigger>
<Trigger Property="IsEnabled" Value="False">
<Setter Property="Stroke" TargetName="circle" Value="#FFBCBCBC"/>
<Setter Property="Fill" TargetName="circle" Value="#FFE6E6E6"/>
<Setter Property="Stroke" TargetName="arrow" Value="#FF707070"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Setter.Value>
</Setter>
</Trigger>
<Trigger Property="ExpandDirection" Value="Up">
<Setter Property="DockPanel.Dock" TargetName="ExpandSite" Value="Top"/>
<Setter Property="DockPanel.Dock" TargetName="HeaderSite" Value="Bottom"/>
<Setter Property="Style" TargetName="HeaderSite">
<Setter.Value>
<Style TargetType="{x:Type ToggleButton}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ToggleButton}">
<Border Padding="{TemplateBinding Padding}">
<Grid Background="Transparent" SnapsToDevicePixels="False">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="19"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<Grid>
<Grid.LayoutTransform>
<TransformGroup>
<RotateTransform Angle="180"/>
</TransformGroup>
</Grid.LayoutTransform>
<Ellipse x:Name="circle" Fill="White" HorizontalAlignment="Center" Height="19" Stroke="#FF333333" VerticalAlignment="Center" Width="19"/>
<Path x:Name="arrow" Data="M1,1.5L4.5,5 8,1.5" HorizontalAlignment="Center" SnapsToDevicePixels="False" Stroke="#FF333333" StrokeThickness="2" VerticalAlignment="Center"/>
</Grid>
<ContentPresenter ContentTemplate="{TemplateBinding ContentTemplate}" Content="{TemplateBinding Content}" Grid.Column="1" ContentStringFormat="{TemplateBinding ContentStringFormat}" HorizontalAlignment="Left" Margin="4,0,0,0" RecognizesAccessKey="True" SnapsToDevicePixels="True" VerticalAlignment="Center"/>
</Grid>
</Border>
<ControlTemplate.Triggers>
<Trigger Property="IsChecked" Value="True">
<Setter Property="Data" TargetName="arrow" Value="M1,4.5L4.5,1 8,4.5"/>
</Trigger>
<Trigger Property="IsMouseOver" Value="True">
<Setter Property="Stroke" TargetName="circle" Value="#FF5593FF"/>
<Setter Property="Fill" TargetName="circle" Value="#FFF3F9FF"/>
<Setter Property="Stroke" TargetName="arrow" Value="Black"/>
</Trigger>
<Trigger Property="IsPressed" Value="True">
<Setter Property="Stroke" TargetName="circle" Value="#FF3C77DD"/>
<Setter Property="StrokeThickness" TargetName="circle" Value="1.5"/>
<Setter Property="Fill" TargetName="circle" Value="#FFD9ECFF"/>
<Setter Property="Stroke" TargetName="arrow" Value="Black"/>
</Trigger>
<Trigger Property="IsEnabled" Value="False">
<Setter Property="Stroke" TargetName="circle" Value="#FFBCBCBC"/>
<Setter Property="Fill" TargetName="circle" Value="#FFE6E6E6"/>
<Setter Property="Stroke" TargetName="arrow" Value="#FF707070"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Setter.Value>
</Setter>
</Trigger>
<Trigger Property="ExpandDirection" Value="Left">
<Setter Property="DockPanel.Dock" TargetName="ExpandSite" Value="Left"/>
<Setter Property="DockPanel.Dock" TargetName="HeaderSite" Value="Right"/>
<Setter Property="Style" TargetName="HeaderSite">
<Setter.Value>
<Style TargetType="{x:Type ToggleButton}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ToggleButton}">
<Border Padding="{TemplateBinding Padding}">
<Grid Background="Transparent" SnapsToDevicePixels="False">
<Grid.RowDefinitions>
<RowDefinition Height="19"/>
<RowDefinition Height="*"/>
</Grid.RowDefinitions>
<Grid>
<Grid.LayoutTransform>
<TransformGroup>
<RotateTransform Angle="90"/>
</TransformGroup>
</Grid.LayoutTransform>
<Ellipse x:Name="circle" Fill="White" HorizontalAlignment="Center" Height="19" Stroke="#FF333333" VerticalAlignment="Center" Width="19"/>
<Path x:Name="arrow" Data="M1,1.5L4.5,5 8,1.5" HorizontalAlignment="Center" SnapsToDevicePixels="False" Stroke="#FF333333" StrokeThickness="2" VerticalAlignment="Center"/>
</Grid>
<ContentPresenter ContentTemplate="{TemplateBinding ContentTemplate}" Content="{TemplateBinding Content}" ContentStringFormat="{TemplateBinding ContentStringFormat}" HorizontalAlignment="Center" Margin="0,4,0,0" Grid.Row="1" RecognizesAccessKey="True" SnapsToDevicePixels="True" VerticalAlignment="Top"/>
</Grid>
</Border>
<ControlTemplate.Triggers>
<Trigger Property="IsChecked" Value="True">
<Setter Property="Data" TargetName="arrow" Value="M1,4.5L4.5,1 8,4.5"/>
</Trigger>
<Trigger Property="IsMouseOver" Value="True">
<Setter Property="Stroke" TargetName="circle" Value="#FF5593FF"/>
<Setter Property="Fill" TargetName="circle" Value="#FFF3F9FF"/>
<Setter Property="Stroke" TargetName="arrow" Value="Black"/>
</Trigger>
<Trigger Property="IsPressed" Value="True">
<Setter Property="Stroke" TargetName="circle" Value="#FF3C77DD"/>
<Setter Property="StrokeThickness" TargetName="circle" Value="1.5"/>
<Setter Property="Fill" TargetName="circle" Value="#FFD9ECFF"/>
<Setter Property="Stroke" TargetName="arrow" Value="Black"/>
</Trigger>
<Trigger Property="IsEnabled" Value="False">
<Setter Property="Stroke" TargetName="circle" Value="#FFBCBCBC"/>
<Setter Property="Fill" TargetName="circle" Value="#FFE6E6E6"/>
<Setter Property="Stroke" TargetName="arrow" Value="#FF707070"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Setter.Value>
</Setter>
</Trigger>
<Trigger Property="IsEnabled" Value="False">
<Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>

<Expander Name="EXPANDER_NAME">
<Expander IsExpanded="True" Margin="0">
<Expander.Header>
<Grid Background="Red" Width="{Binding ElementName=EXPANDER_NAME, Path=ActualWidth}">
<Grid.ColumnDefinitions>
<ColumnDefinition/>
<ColumnDefinition Width="30"/>
</Grid.ColumnDefinitions>
<TextBlock> HEADER TEXT <TextBlock>
</Grid>
</Expander.Header>
</Expander>

I Agree with HTH - check what sort of a container you're putting the Expander in... the StackPanel will always fold it's children down to the smallest size they can go to.
I'm using Expanders a lot in my project, and if you drop them into a Grid / DockPanel, then the expander will fill all available space (assuming it's Vertical & Horizontal orientations are set to Stretch).
Jonathan's suggestion of Binding the Expander's width to the container's width can get a bit tricky... I tried this technique a few weeks back and found that it can producte undesirable results in some cases, because it can inhibit the functioning of the layout system.
PS: As a general tip (and I'm sure I'm gonna get flamed for writing this), if you're unsure of what sort of layout-container to your controls in, then start off with a Grid. Using the Column & Row definitions allows you to very easily control whether child controls use minimum space ("Auto"), maximum space ("*") or an exact amount of space ("[number]").

The Silverlight Toolkit includes an Accordion control which acts like an expander that always stretches to the available space. I haven't tested it yet, but it might be functional for WPF too, like the Silverlight Chart controls.