My dog loathes brindle staffies. She was also very anti-black people, until I needed carers and those the agency sent were all Black Africans (newly immigrated). It took a while, and she still suspiciously stalks my female carer and puts herself between us protectively (female carer is loud, brash, prefers to be rude to me in a "joking" fashion)... but the male carer, my dog absolutely adores. I'm pretty sure if he were to ask her to run away with him, I'd not get a backwards glance... (He's quiet, smiley, likes to chat with the dog about his week and young children - she literally trots along at his heels whilst he works, with her tail up and wagging)
My dog is also a rescue, abuse before 8/9 weeks old. She's 7 years old now, and is - ironically - a black Kokoni!
My parents dog, however, is not a rescue, is 7.5 years old, has been in the family since he was 10 weeks old. He is extremely racist... but then, so are my parents (although they deny it vehemently). Their neighbour is Ugandan, has lived in her house longer than my parents have been in theirs (30 years), but they talk about her as though she moved in and spoilt the street they all live in. I just figure that their dog is picking up on their vibes of intolerance and, so, barking at anyone who isn't white. It can be excruciating, because they reward the dog for barking, so, of course, he keeps on doing it...
Having said that, my mother was also adamant that her dog hates all black dogs... but he and mine get along just fine. My mother's excuse? "Well, she's family...". Like that makes a difference. My other dog, a Spaniel, was terrified of black Labs - but that was because he was attacked by one as a puppy. No idea why my current dog hates brindle staffies, when she loves or tolerates all other breeds and fur colours of dogs - but assume one did something to her before she came to us.