I was thinking, perhaps if you know of prominent black web sites that list black artist and where their works are posted.
I know the internet sort of homogenizes all artist into style groupings and African-American art/artist are not a style grouping. It says that black artist are not special any more than other artist. The internet becomes a level playing field, we become just other artist.
But, from a marketing standpoint, to be able to identify the works of black artist is very important to folks predisposed in that direction. Exposure is good but you also have to target an audience and get their attention. You yourself have to say "I am a black artist and my stuff is here!".
I recommend custom artist postcards, business cards and invitation letters that you can send out to your network, and to perspective clients and buyers. Any internet gallery tends to be global but not magic. You have to work the magic and market your self. Think of the gallery as a repository rather than a marketing firm. You want to say "my gallery is here", not come look at all the stuff on this site, oh yeah, my stuff is there too.