Retread?
People like hiring, generally, coaches with track records. An unproven black coach is in the same boat as an unproven white coach: Unproven. How, with no track record, are you determining that those minority coaches that are passed over ARE qualified?
If you are a School athletic director, who is under intense pressure to win, are you going to hire someone you know has won before and has a track record you can look at and a name your boosters will recognize. . . or are you going to hire an unknown who might or might not turn out to be good - you don't know because he doesn't have a track record?
I seriously doubt that in 99.99% of cases race has even the SLIGHTEST bit to do with it.