My bunny gets orange on her chin and chest from carrots, I just leave it. she grooms herself so much that it just disappears in a day or two anyway.

There is stuff on the market called Bunny Bath (I think I have the name right) one is a shampoo (liquid) and the other is a dry powder. Most rabbits groom themselves pretty thoroughly though, I wouldn't bather her unless there was an absolute need for it. Rabbits don't like water (except to drink)