I love the three black models in My Dorm (Sam, Simone, and Kim).
I guess what you say about black girls ending up as side girls is because of the player (and dev) base. Most (non HS) games feature Caucasian girls because the feeling out there is that it's what the audience wants. Or what the devs like.
In my case, I love all kinds of women (who would have guessed?), and, although the game is majorly Caucasian, there is an Asian (2 in the future), an Indian (2 in the future), a Hispanic (2 in the future), and three black women. 32% (9/28) non-Caucasian girls.
I could have added more, but it would be hard, since the core family+Amanda+Eva already add up to another 9 girls. Only 10 more spots (3 Caucasian students in each batch, Kiara, Eileen, Megan, and Scarlett). I wouldn't replace any of those girls.