No, so far you have been mostly correct. I bought up a similar question a while ago and one of the posters best explained it that many of the witches seen thus far on Vampire Diaries are related to two black families (Bonnie's and that the two guys-can't remember their names). That doesn't account for Gina Torres though. The poster also informed me that there were white witches on VD as well, though I hadn't seen the episodes with them on. And the Secret Circle-the companion show-features white witches.
I think there was at least one black vampire that escaped from that pit last year (can't remember if I saw that or if the poster pointed that out to me. We also have Kelly Hu and her daughter as vamps). It would be nice though to see a bit more diversity among the supernatural on VD though.