Animated GradientStop Opacity
<Window x:Class="WpfApplication1.ShapesWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="ShapesWindow" Height="160" Width="400"> <Window.Resources> <Style TargetType="{x:Type TextBlock}"> <Setter Property="Background" Value="White" /> <Setter Property="Padding" Value="10" /> <Setter Property="BitmapEffect"> <Setter.Value> <OuterGlowBitmapEffect GlowColor="White" /> </Setter.Value> </Setter> </Style> <Style TargetType="{x:Type Rectangle}"> <Setter Property="BitmapEffect"> <Setter.Value> <DropShadowBitmapEffect /> </Setter.Value> </Setter> </Style> </Window.Resources> <StackPanel> <Rectangle Width="200" Height="100" Stroke="Black" StrokeThickness="1" Margin="10"> <Rectangle.Fill> <LinearGradientBrush> <GradientStop Color="MediumBlue" Offset="0.0" /> <GradientStop x:Name="gradientStopC2" Color="Purple" Offset="0.5" /> <GradientStop Color="Red" Offset="1.0" /> </LinearGradientBrush> </Rectangle.Fill> <Rectangle.Triggers> <EventTrigger RoutedEvent="Rectangle.MouseLeftButtonDown"> <BeginStoryboard> <Storyboard> <ColorAnimation Storyboard.TargetName="gradientStopC2" Storyboard.TargetProperty="Color" Duration="0:0:3" FillBehavior="Stop"> <ColorAnimation.By> <Color ScA="-1" ScR="0" ScB="0" ScG="0" /> </ColorAnimation.By> </ColorAnimation> </Storyboard> </BeginStoryboard> </EventTrigger> </Rectangle.Triggers> </Rectangle> </StackPanel> </Window>