Ron Paul has proven that he doesn't mind sharing a vision that goes against the mainstream, time and time again. EVERYBODY, liberals, neo-cons, you name it will agree on that one.
So, if he were a racist at all, he would be arguing for race inequality the whole time. He doesn't, which in his case means he isn't racist. Actually one cannot say the same thing of the other candidates.
Nicely explains why he has the black vote as well.