> don't expose Color or Brush properties Why not? The ViewModel is written specifically for the View, and it does not serve any purpose to make it UI independe

> don't expose Color or Brush properties Why not? The ViewModel is written specifically for the View, and it does not serve any purpose to make it UI independent. By avoiding Color etc. in this layer you end with two UI independent layers (Model and ViewModel) and that makes no sense. One UI-independent layer is enough. In MVVM the View knows about the ViewModel but supposedly the ViewModel does not know about the View. But in reality the ViewModel is written specifically for the View, so it might as well know the View.