Specify a brush with the expanded XAML syntax
<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'> <Canvas xmlns="http://schemas.microsoft.com/client/2007"> <Rectangle StrokeThickness="10" Canvas.Left="96" Canvas.Top="160" Width="256" Height="224" > <Rectangle.Fill> <SolidColorBrush Color="Blue"/> </Rectangle.Fill> <Rectangle.Stroke> <SolidColorBrush Color="Black"/> </Rectangle.Stroke> </Rectangle> </Canvas> </UserControl>