Cambiar Automáticamente de color una Ellipse

Código XAML

<Window.Triggers>
<EventTrigger RoutedEvent="Window.Loaded">
<EventTrigger.Actions>
<BeginStoryboard>
<Storyboard>
<ColorAnimation Storyboard.TargetName="myEllipse" Storyboard.TargetProperty="(Ellipse.Fill).(SolidColorBrush.Color)" Duration="0:0:5" From="Black" To="White" RepeatBehavior="Forever" AutoReverse="True"/>
</Storyboard>
</BeginStoryboard>
</EventTrigger.Actions>
</EventTrigger>
</Window.Triggers>
<Ellipse x:Name="myEllipse" Fill="Black"/>