I'm white so I can't speak to the racism part, but I can to the female friends part. Many girls get less catty and mean as they mature. I'd say mid-late 20s is when a lot of girls start finding it easier to make female friends. Of course, some women will always be insecure mean-girls and that may manifest in new ways from how it did in high school, but there are many people who grow into confident, kind, supportive adults. It may take a few years before these types of people outnumber the shitty ones.

As for the racism, do you live in a majority-white area? If so I imagine that's difficult and you may want to consider moving to a more diverse area where you could reduce some of the stress around anticipating racism by having more opportunities to meet black women for friends.