My neighbors are originally from Nigeria. I have a female doberman mix who is excitable yet nice enough to be a good family pet. Once, their kids came over to play with my brother, and my dog started going ballistic. Usually when she sees a new face she’ll bark excitedly, but she was growling and snarling like mad and literally ripping at the chainlink gate with her teeth trying to get at them. This puzzled me greatly, and after a bit of research I discovered that since dogs only see in black and white, a person with very dark skin literally looks like a solid shadow to them. They can’t distinguish the person’s facial features or bodily form, so they basically think they’re seeing a poltergeist. So naturally, dogs that are not used to being around dark-skinned people are more likely to get hostile when they do see someone, which is why many black people are nervous around dogs. Also, I remember having to protect this small kid I was mentoring at the time (who happened to be black) from some Nazi redneck guy who was trying to sic his pitbull on him (yeah, that’s reeaal brave), so remember that such hostility didn’t die with segregation.