Skinning: Using a Color as StaticResource for another Color

This?

<Color x:Key="DarkBrown">#C4AF8D</Color>

<DynamicResource x:Key="TextBoxBackgroundColor" ResourceKey="DarkBrown"/>
<DynamicResource x:Key="ToolBarButtonForegroundColor" ResourceKey="DarkBrown"/>

For more advanced use cases and multiple levels of aliasing see this answer.