@Anonymous, just thought I add something else for your consideration. Kind of a hybrid of @Anonymous workflow and mine. Still use Parts, but use view overrides for wall (in course detail view) to change the outer most finish layer, not to a hidden line (not to white) and the transparency to 100%. That way you can have a representation of the finish extents of the wall in view, while accentuating the core (perhaps with a poche or heavier pen weight). You would have to set the view to show both Parts and Original as well, for this to work.
(Sorry,i f that sounds a bit cryptic. Hope you get it)