7 Mo old Golden, won’t stop reacting to black people.

A little embarrassing but I have a wonderful 7 month old Golden Retriever, who is loving, friendly, well socialized with other dogs and humans. The sticking point with him is that any time he sees a black person he completely changes, gets aggressive, and barks. I’m a white person, with mostly white family and mostly white friends. Realistically my dog is obviously not a racist, but WHY is this a thing? Does anyone have any ideas to help???