This dependency's caused by PBColorPreferenceView referencing
UpdatingRectangleMorph (subclass of RectangleMorph).

Would it make sense to move this class to Morphic, home of RectangleMorph?

That would leave a single source code based dependency on EToys, from
GetText's use of EToy's Vocabulary work. (The qualifier's because
Presenter >> #defaultPresenterClass causes a dependency because it
return EtoysPresenter. That's easily removed by executing `Presenter
defaultPresenterClass: nil`, which in fact Etoys does when you unload
it.)

frank