I agree with the others before me this is not truly racism, but I do see what you mean. That is a bit of a pattern in the Mate Center. I know when I go to Mate Center just to hang out or have fun with the people I just go, and sit where there might be an open spot for me to rest in. Though you are correct. The pattern is a bit strange, but again as the others said I think it's just mostly a color preference. That and people tend to sit as close as they can to the male/female they wish to be their mate.
I don't think it's a form of 'racism' since in generality wolves are a universal race its own. Not only that they're not declaring any form of stating "A black pelted wolf is inferior or superior to a brown naturalistic wolf", ultimately it's just personal preference, as many have stated.
Though I have noticed, a mild bit of segregation in regards of groups, if you don't have a naturalistic fur pallet *Such as if you don't have another color to counterbalance the black* you were denied group acceptance. Which I find personally puzzling but you know. Whatever strums your strings?