Есть ли у вас Expression Blend? Это можно легко сделать, щелкнув правой кнопкой мыши ToggleButton и выбрав «Редактировать шаблон», затем «Редактировать копию ...» Из шаблона перейдите на вкладку «Состояния» и выберите состояние «Проверено». Сбросьте цвет фона, отличающийся от базового состояния и готово.
См. Образец:
<Window.Resources>
<Style x:Key="ButtonFocusVisual">
<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>
<LinearGradientBrush x:Key="ButtonNormalBackground" EndPoint="0,1" StartPoint="0,0">
<GradientStop Color="#F3F3F3" Offset="0"/>
<GradientStop Color="#EBEBEB" Offset="0.5"/>
<GradientStop Color="#DDDDDD" Offset="0.5"/>
<GradientStop Color="#CDCDCD" Offset="1"/>
</LinearGradientBrush>
<SolidColorBrush x:Key="ButtonNormalBorder" Color="#FF707070"/>
<Style x:Key="ToggleButtonStyle" TargetType="{x:Type ToggleButton}">
<Setter Property="FocusVisualStyle" Value="{StaticResource ButtonFocusVisual}"/>
<Setter Property="Background" Value="{StaticResource ButtonNormalBackground}"/>
<Setter Property="BorderBrush" Value="{StaticResource ButtonNormalBorder}"/>
<Setter Property="BorderThickness" Value="1"/>
<Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}"/>
<Setter Property="HorizontalContentAlignment" Value="Center"/>
<Setter Property="VerticalContentAlignment" Value="Center"/>
<Setter Property="Padding" Value="1"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ToggleButton}">
<Microsoft_Windows_Themes:ButtonChrome x:Name="Chrome" BorderBrush="{TemplateBinding BorderBrush}" RenderMouseOver="{TemplateBinding IsMouseOver}" RenderPressed="{TemplateBinding IsPressed}" RenderDefaulted="{TemplateBinding Button.IsDefaulted}" SnapsToDevicePixels="true" Background="White">
<VisualStateManager.VisualStateGroups>
<VisualStateGroup x:Name="CommonStates" ei:ExtendedVisualStateManager.UseFluidLayout="True">
<VisualStateGroup.Transitions>
<VisualTransition GeneratedDuration="0:0:0.5"/>
</VisualStateGroup.Transitions>
</VisualStateGroup>
<VisualStateGroup x:Name="CheckStates">
<VisualState x:Name="Checked">
<Storyboard>
<ColorAnimationUsingKeyFrames Storyboard.TargetProperty="(Panel.Background).(SolidColorBrush.Color)" Storyboard.TargetName="Chrome">
<EasingColorKeyFrame KeyTime="0" Value="Red"/>
</ColorAnimationUsingKeyFrames>
</Storyboard>
</VisualState>
<VisualState x:Name="Unchecked"/>
<VisualState x:Name="Indeterminate"/>
</VisualStateGroup>
</VisualStateManager.VisualStateGroups>
<VisualStateManager.CustomVisualStateManager>
<ei:ExtendedVisualStateManager/>
</VisualStateManager.CustomVisualStateManager>
<ContentPresenter HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="{TemplateBinding Padding}" RecognizesAccessKey="True" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" VerticalAlignment="{TemplateBinding VerticalContentAlignment}"/>
</Microsoft_Windows_Themes:ButtonChrome>
<ControlTemplate.Triggers>
<Trigger Property="IsKeyboardFocused" Value="true">
<Setter Property="RenderDefaulted" TargetName="Chrome" Value="true"/>
</Trigger>
<Trigger Property="IsChecked" Value="true">
<Setter Property="RenderPressed" TargetName="Chrome" Value="true"/>
</Trigger>
<Trigger Property="IsEnabled" Value="false">
<Setter Property="Foreground" Value="#ADADAD"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Window.Resources>
<Grid x:Name="LayoutRoot">
<ToggleButton Content="ToggleButton" HorizontalAlignment="Left" Height="36" Margin="116,131,0,0" VerticalAlignment="Top" Width="122" Background="White" Style="{DynamicResource ToggleButtonStyle}"/>
</Grid>