Speaking as a black person, Herman Cain and Allen West are nuckin' futs. So-called black conservatives are like the crazy uncle in the corner at Thanksgiving who rants about everything for a while and then everyone ignores him and goes on with the holiday.
Blacks are pretty conservative overall; many are one or two generations from the farm, lower educations, working class, have military folks in our families, we are raised to respect honest work, god, apple pie, the flag and all that. The repubs should have it easy getting black votes. Colin Powell as a repub might have gotten some traction, because: He. Was. Not. Crazy.
If the repubs ever start fielding more folks of color who are Not Crazy, they might be able to do some real damage to the lock the dems have on the people of color vote. But I don't think they will be able to move beyond the occasional black or brown wingnut token. There is too much racist crap bubbling around the conservative cauldron to allow people of color real power and authority in the party.
What black or brown person in their right mind would want to hang out with a bunch of armed tea partiers carrying pictures of Obama with a bone in his nose? Doesn't make anyone promoting that crap look attractive to anyone who looks a bit like Obama.
And so it goes.