I disagree. The intimate and personal nature of the work should allow for freedom of preference. Serving someone a sandwich doesn't require penetration or swapping body fluid. It may be the only kind of work where race (actually it's body shape, size, color) DOES affect the person offering the service and how they deliver it.
A prostitute may well be a racist, but because it's the most intimate of arts, her preferences on appearance, size, shape, etc., should be the first consideration here regardless of her prejudices.