Animate the Color of a Brush with Indirect Property Targeting

   
     
<Window x:Class="Main"
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  Title="" Height="300" Width="300"
  Background="Black">
  <Window.Triggers>
    <EventTrigger RoutedEvent="Window.Loaded">
      <BeginStoryboard>
        <Storyboard AutoReverse="True" RepeatBehavior="Forever">
          <ColorAnimation Storyboard.TargetProperty="Background.Color" To="White" />
          <ColorAnimation Storyboard.TargetName="bd" Storyboard.TargetProperty="Background.(SolidColorBrush.Color)" To="Black" />
        </Storyboard>
      </BeginStoryboard>
    </EventTrigger>
  </Window.Triggers>
  <Border x:Name="bd" Margin="20" Background="HotPink">
    <Rectangle x:Name="rect" Width="100" Height="100" Fill="WhiteSmoke" />
  </Border>
</Window>