Specify Alpha, Red, Green and Blue using scARGB format
<UserControl x:Class='SilverlightApplication3.MainPage'
xmlns='http://schemas.microsoft.com/winfx/2006/xaml/presentation'
xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'
xmlns:d='http://schemas.microsoft.com/expression/blend/2008'
xmlns:mc='http://schemas.openxmlformats.org/markup-compatibility/2006'
mc:Ignorable='d'
d:DesignWidth='640'
d:DesignHeight='480'>
<Grid x:Name="LayoutRoot" Background="White">
<StackPanel>
<Rectangle Width="200"
Height="140"
Fill="sc#1.0, 0.3, 0.8, 0.2" />
</StackPanel>
</Grid>
</UserControl>
Related examples in the same category