I agree with CantDraw about taking the visible clothing (necktie, vest) all the way up. His legs look a little short to me. Maybe extend his lower body down just a bit further.
As far as coloring: Any shading that you do I would keep minimal and on the edges. Like maybe just the top hat, shoulders, the very tips/outside edges of the cape. The flat black is really working for this guy. 
Great design!
