Yes Grand Theft Auto IV is a cool game. But a " Big Tutorial " some people call it. I once found a guy got pulled over on the Bridge from South Bohan to Algonquin for a traffic check. He once said " You drive like a reckless asshole.
Back on topic.
The people that you mention are indeed gang members. There are quite a number of African American gangs, including the M.O.B , North Holland Hustlers , and a few more. Each gang has a diffrent skin. In this case a character. Like the M.O.B has people with Brown pants with a white T-Shirt and White jacket, and gold chain.