<Rectangle xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation">
<Rectangle.Fill>
			<RadialGradientBrush GradientOrigin="0.5,0.5" Center="0.5,0.5" 
          RadiusX="0.5" RadiusY="0.5" >
				<GradientStop Color="Green" Offset="0.0" />
				<GradientStop Color="Red" Offset="0.25" />
				<GradientStop Color="Yellow" Offset="0.5" />
				<GradientStop Color="Blue" Offset="1.0" />
			</RadialGradientBrush>
		</Rectangle.Fill>
	</Rectangle>