Fear of black men?

My friend just recently rescued a pit bull from her work who is about 2-3 years old. He is very friendly and sweet towards everyone and extremely well trained, but seems very scared of grown black men.

Is there any way to desensitize dogs who are afraid like this? We are assuming that the dog was probably treated pretty poorly prior to his foster mom rescuing him from the pound.

My friend is really bummed out because the man that this dog is afraid of may become her new roommate soon, and she doesn't want to have to give dog back to the rescue organization or continue to traumatize it by having him over there every day.