How do you reference a system theme ResourceDictionary resource in generic.xaml?

I "think" I've merged the ResourceDictionary properly:

<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="/PresentationFramework.Aero2;component/themes/aero2.normalcolor.xaml" />
</ResourceDictionary.MergedDictionaries>

Now how do I reference one of the brushes defined in it?