Try this style and change the fill color in the CheckIcon rectangle.
<Style TargetType="CheckBox"> <Setter Property="Background" Value="#FF448DCA"/> <Setter Property="Foreground" Value="#FF000000"/> <Setter Property="HorizontalContentAlignment" Value="Left"/> <Setter Property="VerticalContentAlignment" Value="Top"/> <Setter Property="Padding" Value="4,1,0,0"/> <Setter Property="BorderThickness" Value="1"/> <Setter Property="BorderBrush"> <Setter.Value> <LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0"> <GradientStop Color="#FFA3AEB9" Offset="0"/> <GradientStop Color="#FF8399A9" Offset="0.375"/> <GradientStop Color="#FF718597" Offset="0.375"/> <GradientStop Color="#FF617584" Offset="1"/> </LinearGradientBrush> </Setter.Value> </Setter> <Setter Property="Template"> <Setter.Value> <ControlTemplate TargetType="CheckBox"> <Grid> <Grid.ColumnDefinitions> <ColumnDefinition Width="16"/> <ColumnDefinition Width="*"/> </Grid.ColumnDefinitions> <vsm:VisualStateManager.VisualStateGroups> <vsm:VisualStateGroup x:Name="CommonStates"> <vsm:VisualState x:Name="Normal"/> <vsm:VisualState x:Name="MouseOver"> <Storyboard> <DoubleAnimation Storyboard.TargetName="BackgroundOverlay" Storyboard.TargetProperty="Opacity" Duration="0" To="1"/> <DoubleAnimation Storyboard.TargetName="BoxMiddleBackground" Storyboard.TargetProperty="Opacity" Duration="0" To="1"/> <ColorAnimation Storyboard.TargetName="BoxMiddle" Storyboard.TargetProperty="(Shape.Fill).(GradientBrush.GradientStops)[3].(GradientStop.Color)" Duration="0" To="#7FFFFFFF"/> <ColorAnimation Storyboard.TargetName="BoxMiddle" Storyboard.TargetProperty="(Shape.Fill).(GradientBrush.GradientStops)[2].(GradientStop.Color)" Duration="0" To="#CCFFFFFF"/> <ColorAnimation Storyboard.TargetName="BoxMiddle" Storyboard.TargetProperty="(Shape.Fill).(GradientBrush.GradientStops)[1].(GradientStop.Color)" Duration="0" To="#F2FFFFFF"/> </Storyboard> </vsm:VisualState> <vsm:VisualState x:Name="Pressed"> <Storyboard> <DoubleAnimation Storyboard.TargetName="BackgroundOverlay" Storyboard.TargetProperty="Opacity" Duration="0" To="1"/> <DoubleAnimation Storyboard.TargetName="BoxMiddleBackground" Storyboard.TargetProperty="Opacity" Duration="0" To="1"/> <ColorAnimation Storyboard.TargetName="BoxMiddle" Storyboard.TargetProperty="(Shape.Fill).(GradientBrush.GradientStops)[3].(GradientStop.Color)" Duration="0" To="#6BFFFFFF"/> <ColorAnimation Storyboard.TargetName="BoxMiddle" Storyboard.TargetProperty="(Shape.Fill).(GradientBrush.GradientStops)[2].(GradientStop.Color)" Duration="0" To="#C6FFFFFF"/> <ColorAnimation Storyboard.TargetName="BoxMiddle" Storyboard.TargetProperty="(Shape.Fill).(GradientBrush.GradientStops)[1].(GradientStop.Color)" Duration="0" To="#EAFFFFFF"/> <ColorAnimation Storyboard.TargetName="BoxMiddle" Storyboard.TargetProperty="(Shape.Fill).(GradientBrush.GradientStops)[0].(GradientStop.Color)" Duration="0" To="#F4FFFFFF"/> <ColorAnimation Storyboard.TargetName="BoxMiddle" Storyboard.TargetProperty="(Shape.Stroke).(GradientBrush.GradientStops)[3].(GradientStop.Color)" Duration="0" To="#FF6DBDD1"/> <ColorAnimation Storyboard.TargetName="BoxMiddle" Storyboard.TargetProperty="(Shape.Stroke).(GradientBrush.GradientStops)[0].(GradientStop.Color)" Duration="0" To="#FF6DBDD1"/> <ColorAnimation Storyboard.TargetName="BoxMiddle" Storyboard.TargetProperty="(Shape.Stroke).(GradientBrush.GradientStops)[1].(GradientStop.Color)" Duration="0" To="#FF6DBDD1"/> <ColorAnimation Storyboard.TargetName="BoxMiddle" Storyboard.TargetProperty="(Shape.Stroke).(GradientBrush.GradientStops)[2].(GradientStop.Color)" Duration="0" To="#FF6DBDD1"/> </Storyboard> </vsm:VisualState> <vsm:VisualState x:Name="Disabled"> <Storyboard> <DoubleAnimation Storyboard.TargetName="contentPresenter" Storyboard.TargetProperty="(UIElement.Opacity)" Duration="0" To=".55"/> <DoubleAnimation Storyboard.TargetName="DisabledVisualElement" Storyboard.TargetProperty="(UIElement.Opacity)" Duration="0" To="0.55"/> </Storyboard> </vsm:VisualState> </vsm:VisualStateGroup> <vsm:VisualStateGroup x:Name="CheckStates"> <vsm:VisualState x:Name="Checked"> <Storyboard> <DoubleAnimation Storyboard.TargetName="CheckIcon" Storyboard.TargetProperty="(UIElement.Opacity)" Duration="0" To="1"/> </Storyboard> </vsm:VisualState> <vsm:VisualState x:Name="Unchecked"/> <vsm:VisualState x:Name="Indeterminate"> <Storyboard> <DoubleAnimation Storyboard.TargetName="IndeterminateIcon" Storyboard.TargetProperty="(UIElement.Opacity)" Duration="0" To="1"/> </Storyboard> </vsm:VisualState> </vsm:VisualStateGroup> <vsm:VisualStateGroup x:Name="FocusStates"> <vsm:VisualState x:Name="Focused"> <Storyboard> <DoubleAnimation Storyboard.TargetName="ContentFocusVisualElement" Storyboard.TargetProperty="Opacity" Duration="0" To="1"/> </Storyboard> </vsm:VisualState> <vsm:VisualState x:Name="Unfocused" /> </vsm:VisualStateGroup> <vsm:VisualStateGroup x:Name="ValidationStates"> <vsm:VisualState x:Name="Valid"/> <vsm:VisualState x:Name="InvalidUnfocused"> <Storyboard> <ObjectAnimationUsingKeyFrames Storyboard.TargetName="ValidationErrorElement" Storyboard.TargetProperty="Visibility"> <DiscreteObjectKeyFrame KeyTime="0" > <DiscreteObjectKeyFrame.Value> <Visibility>Visible</Visibility> </DiscreteObjectKeyFrame.Value> </DiscreteObjectKeyFrame> </ObjectAnimationUsingKeyFrames> </Storyboard> </vsm:VisualState> <vsm:VisualState x:Name="InvalidFocused"> <Storyboard> <ObjectAnimationUsingKeyFrames Storyboard.TargetName="ValidationErrorElement" Storyboard.TargetProperty="Visibility"> <DiscreteObjectKeyFrame KeyTime="0" > <DiscreteObjectKeyFrame.Value> <Visibility>Visible</Visibility> </DiscreteObjectKeyFrame.Value> </DiscreteObjectKeyFrame> </ObjectAnimationUsingKeyFrames> <ObjectAnimationUsingKeyFrames Storyboard.TargetName="validationTooltip" Storyboard.TargetProperty="IsOpen"> <DiscreteObjectKeyFrame KeyTime="0" > <DiscreteObjectKeyFrame.Value> <sys:Boolean>True</sys:Boolean> </DiscreteObjectKeyFrame.Value> </DiscreteObjectKeyFrame> </ObjectAnimationUsingKeyFrames> </Storyboard> </vsm:VisualState> </vsm:VisualStateGroup> </vsm:VisualStateManager.VisualStateGroups> <Grid HorizontalAlignment="Left" VerticalAlignment="Top"> <Rectangle x:Name="Background" Width="14" Height="14" RadiusX="1" RadiusY="1" Stroke="{TemplateBinding BorderBrush}" StrokeThickness="{TemplateBinding BorderThickness}" Fill="#FFFFFFFF" Margin="1"/> <Rectangle x:Name="BackgroundOverlay" Fill="#FFC4DBEE" Opacity="0" Width="14" Height="14" RadiusX="1" RadiusY="1" StrokeThickness="1" Margin="1" Stroke="#00000000"/> <Rectangle x:Name="BoxMiddleBackground" Width="10" Height="10" RadiusX="1" RadiusY="1" Fill="{TemplateBinding Background}" Stroke="#00000000" StrokeThickness="1"/> <Rectangle x:Name="BoxMiddle" Width="10" Height="10" RadiusX="1" RadiusY="1" StrokeThickness="1" > <Rectangle.Stroke> <LinearGradientBrush EndPoint=".5,1" StartPoint=".5,0"> <GradientStop Color="#FFFFFFFF" Offset="1"/> <GradientStop Color="#FFFFFFFF" Offset="0"/> <GradientStop Color="#FFFFFFFF" Offset="0.375"/> <GradientStop Color="#FFFFFFFF" Offset="0.375"/> </LinearGradientBrush> </Rectangle.Stroke> <Rectangle.Fill> <LinearGradientBrush StartPoint="0.62,0.15" EndPoint="0.64,0.88"> <GradientStop Color="#FFFFFFFF" Offset="0.013" /> <GradientStop Color="#F9FFFFFF" Offset="0.375" /> <GradientStop Color="#EAFFFFFF" Offset="0.603" /> <GradientStop Color="#D8FFFFFF" Offset="1" /> </LinearGradientBrush> </Rectangle.Fill> </Rectangle> <Rectangle x:Name="BoxMiddleLine" Width="10" Height="10" RadiusX="1" RadiusY="1" Stroke="{TemplateBinding BorderBrush}" StrokeThickness="1" Opacity=".2"/> <Path x:Name="CheckIcon" Margin="1,1,0,1.5" Fill="#FF333333" Stretch="Fill" Opacity="0" Width="10.5" Height="10" Data="M102.03442,598.79645 L105.22962,597.78918 L106.78825,600.42358 C106.78825,600.42358 108.51028,595.74304 110.21724,593.60419 C112.00967,591.35822 114.89314,591.42316 114.89314,591.42316 C114.89314,591.42316 112.67844,593.42645 111.93174,594.44464 C110.7449,596.06293 107.15683,604.13837 107.15683,604.13837 z" FlowDirection="LeftToRight"/> <Rectangle x:Name="IndeterminateIcon" Height="2" Fill="#FF333333" Opacity="0" Width="6"/> <Rectangle x:Name="DisabledVisualElement" RadiusX="1" RadiusY="1" Width="14" Height="14" Opacity="0" Fill="#FFFFFFFF"/> <Rectangle x:Name="ContentFocusVisualElement" RadiusX="2" RadiusY="2" Stroke="#FF6DBDD1" StrokeThickness="1" Opacity="0" IsHitTestVisible="false" Width="16" Height="16" /> <Border x:Name="ValidationErrorElement" Margin="1" BorderThickness="1" CornerRadius="1" BorderBrush="#FFDB000C" Visibility="Collapsed" ToolTipService.PlacementTarget="{Binding RelativeSource={RelativeSource TemplatedParent}}"> <ToolTipService.ToolTip> <ToolTip x:Name="validationTooltip" Template="{StaticResource ValidationToolTipTemplate}" DataContext="{Binding RelativeSource={RelativeSource TemplatedParent}}" Placement="Right" PlacementTarget="{Binding RelativeSource={RelativeSource TemplatedParent}}"> <ToolTip.Triggers> <EventTrigger RoutedEvent="Canvas.Loaded"> <EventTrigger.Actions> <BeginStoryboard> <Storyboard> <ObjectAnimationUsingKeyFrames Storyboard.TargetName="validationTooltip" Storyboard.TargetProperty="IsHitTestVisible"> <DiscreteObjectKeyFrame KeyTime="0" > <DiscreteObjectKeyFrame.Value> <sys:Boolean>true</sys:Boolean> </DiscreteObjectKeyFrame.Value> </DiscreteObjectKeyFrame> </ObjectAnimationUsingKeyFrames> </Storyboard> </BeginStoryboard> </EventTrigger.Actions> </EventTrigger> </ToolTip.Triggers> </ToolTip> </ToolTipService.ToolTip> <Grid Width="10" Height="10" HorizontalAlignment="Right" Margin="0,-4,-4,0" VerticalAlignment="Top" Background="Transparent"> <Path Margin="0,3,0,0" Data="M 1,0 L5,0 A 2,2 90 0 1 7,2 L7,6 z" Fill="#FFDC000C"/> <Path Margin="0,3,0,0" Data="M 0,0 L2,0 L 7,5 L7,7" Fill="#ffffff"/> </Grid> </Border> </Grid> <ContentPresenter Grid.Column="1" x:Name="contentPresenter" Content="{TemplateBinding Content}" ContentTemplate="{TemplateBinding ContentTemplate}" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" VerticalAlignment="{TemplateBinding VerticalContentAlignment}" Margin="{TemplateBinding Padding}"/> </Grid> </ControlTemplate> </Setter.Value> </Setter>