RadialGradientBrush Opacity from 1 to 0

   
  

<Window x:Class="Workspace.DockExample"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Workspace" Width="640" Height="480">
    <Window.Resources>
        <GradientStopCollection x:Key="myGradientStops">
      <GradientStop Color="Blue" Offset="0.0" />
      <GradientStop Color="Black" Offset="0.5" />
      <GradientStop Color="Transparent" Offset="1.0" />
    </GradientStopCollection>
    </Window.Resources>
    <StackPanel>
    <Rectangle Width="100" Height="50" Stroke="Black" StrokeThickness="1">
      <Rectangle.Fill>
        <RadialGradientBrush GradientStops="{StaticResource myGradientStops}" Opacity="1.0" />
      </Rectangle.Fill>
    </Rectangle>
    <Rectangle Width="100" Height="50" Stroke="Black" StrokeThickness="1" >
      <Rectangle.Fill>
        <RadialGradientBrush GradientStops="{StaticResource myGradientStops}" Opacity="0.75" />
      </Rectangle.Fill>
    </Rectangle>
    <Rectangle Width="100" Height="50" Stroke="Black" StrokeThickness="1">
      <Rectangle.Fill>
        <RadialGradientBrush GradientStops="{StaticResource myGradientStops}" Opacity="0.5" />
      </Rectangle.Fill>
    </Rectangle>
    <Rectangle Width="100" Height="50" Stroke="Black" StrokeThickness="1">
      <Rectangle.Fill>
        <RadialGradientBrush GradientStops="{StaticResource myGradientStops}" Opacity="0.25" />
      </Rectangle.Fill>
    </Rectangle>
    <Rectangle Width="100" Height="50" Stroke="Black" StrokeThickness="1">
      <Rectangle.Fill>
        <RadialGradientBrush GradientStops="{StaticResource myGradientStops}" Opacity="0" />
      </Rectangle.Fill>
    </Rectangle>
    </StackPanel>
</Window>