<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="100" Width="300"> <Grid> <Grid.Resources> <LinearGradientBrush x:Key="VisibleSpectrumBrush" StartPoint="0,0" EndPoint="1,0"> <GradientStop Color="Red" Offset="0.15" /> <GradientStop Color="Orange" Offset="0.2" /> <GradientStop Color="Yellow" Offset="0.35" /> </LinearGradientBrush> </Grid.Resources> <StackPanel> <Rectangle Height="30" Width="280" Fill="{StaticResource VisibleSpectrumBrush}" /> </StackPanel> </Grid> </Window>