<Grid
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
  <Rectangle x:Name="Rect" Height="100" Width="100" Fill="LightGreen" VerticalAlignment="Center" HorizontalAlignment="Center">
    <Rectangle.Triggers>
      <EventTrigger RoutedEvent="Loaded">
        <BeginStoryboard>
          <Storyboard TargetName="Rect" TargetProperty="(Rectangle.Fill).(SolidColorBrush.Color)">
            <ColorAnimation
              BeginTime="0:0:0"
              Duration="0:0:1" From="LightGreen" To="Red"
              RepeatBehavior="10x" 
              AutoReverse="True" />
            <ColorAnimation
              BeginTime="0:0:10"
              Duration="0:0:0.8" From="LightGreen" To="Red"
              RepeatBehavior="12.5x" 
              AutoReverse="True" />
            <ColorAnimation
              BeginTime="0:0:20"
              Duration="0:0:0.4" From="LightGreen" To="Red"
              RepeatBehavior="25x" 
              AutoReverse="True" />
            <ColorAnimation
              BeginTime="0:0:30"
              Duration="0:0:0.2" From="LightGreen" To="Red"
              RepeatBehavior="50x" 
              AutoReverse="True" />
            <ColorAnimation
              BeginTime="0:0:40"
              Duration="0:0:0.1" From="LightGreen" To="Red"
              RepeatBehavior="100x" 
              AutoReverse="True" />
            <ColorAnimation
              BeginTime="0:0:50"
              Duration="0:0:0.05" From="LightGreen" To="Red"
              RepeatBehavior="200x"
              AutoReverse="True" /> 
          </Storyboard>
        </BeginStoryboard>
      </EventTrigger>
    </Rectangle.Triggers>
  </Rectangle>
</Grid>