Perhaps you could simply redirect your child's train of thought. When he says, "That black man over there has a cute dog.", you could say, "Which man? The man with the blue coat on? Yes, the tall man in the blue coat does have a cute dog!" If he sees race is not always the first/most important identifying characteristic, he will unconsciously start to mimic that phrasing.
EXCELLENT!!!!!
You are either a very good parent or someone who will be in the future.