Set color for SolidColorBrush
<Window x:Class="WPFBrushes.ColorAndAlpha" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="Alpha Channel" Height="300" Width="300"> <Grid VerticalAlignment="Center" HorizontalAlignment="Center"> <Rectangle Height="50" Width="50" Stroke="Black" StrokeThickness="4" Margin="4"> <Rectangle.Fill> <SolidColorBrush> <SolidColorBrush.Color> <Color A="0" R="111" G="110" B="0"/> </SolidColorBrush.Color> </SolidColorBrush> </Rectangle.Fill> </Rectangle> </Grid> </Window>