WPF and external resources

[msedi]

The documentation is a bit sparse on that topic. First I have to list up a bit on what I need:

Generic external resource assembly
I have an "root UI" assembly (RootUI.dll) that contains all the resource dictionary to override the default styles and to introduce new colors. But the problem is that not always I need to have the color and style override, so I would like to move the styling and colors outside of the RootUI and put it into an external assembly using the ThemeInfoAttribute(None, External). But its poorly written somewhere how this assembly should be named RootUI.Generic.dll? I couldn't find any comment on this.

Designer
Additionally, does the designer work with an external resource assembly (as given above)?

Resource classes
I would prefer additional classes that contain "direct links" to the resources. A bit similar to SystemColors. So that users of our components do not need to know the key names but instead can reference to something like AppColors.Red or AppBrushes.Red.
I have found a way to do it, but it seems that if I want to choose between StaticResource and DynamicResource and cannot simply return a class lets call it Resource that can be either a StaticResource or a DynamicResource

There of course a lot of standard samples but is there something more elaborate?