Use RGB valued semi-transparent color to paint Ellipse
<Window x:Class="WpfApplication1.Window1" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="WPF" Height="300" Width="300"> <Canvas Margin="5"> <!--RGB semi-transparent color--> <Ellipse Canvas.Top="30" Canvas.Left="90" Fill="#72ff8805" Height="150" Width="100" /> </Canvas> </Window>