An ellipse with a radial fill

   
     

<Window 
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  Title="SolidColorBrush Animation Example"
  Background="White">
  
  <StackPanel>
    <Ellipse  Height ="75" Width ="75">
      <Ellipse.Fill>
        <RadialGradientBrush GradientOrigin="0.5,0.5"
          Center="0.5,0.5" RadiusX="0.5" RadiusY="0.5">
          <GradientStop Color="Yellow" Offset="0" />
          <GradientStop Color="Red" Offset="0.25" />
          <GradientStop Color="Blue" Offset="0.75" />
          <GradientStop Color="LimeGreen" Offset="1" />
        </RadialGradientBrush>
      </Ellipse.Fill>
    </Ellipse>

  </StackPanel>

</Window>