Relative pack URI referring to external component for a Resource
<Window x:Class="UsePackUri.Window1" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="UsePackUri" Height="300" Width="300"> <StackPanel> <StackPanel.Resources> <ResourceDictionary Source="/PresentationFramework.Luna;v3.0.0.0;31bf3856ad364e35;component/themes/luna.normalcolor.xaml" /> </StackPanel.Resources> <Button Content="Luna" /> <CheckBox Content="Theme" /> </StackPanel> </Window>