I don't think a bike tire can be shaved for 2 reasons:
1. I dont think there is any white under a solid black tire. On cars, the white wall is usually a thin one and the rest of the sidewall is literally shaved down to expose more of the white underneath. I've seen some that looked good, and some that the black still bleeds through the white, giving it a dirty look that constantly needs to be cleaned. I've also seen some that the white that was shaved does not match the white that was the original white wall.
2. bike tire sidewalls are really thin, and I wouldn't want to risk making it thinner. For the money you are going to spend on materials, you could probably buy some whites for the same money, if not less.