Oftentimes even that particular one Black will see to it no one else benefits from the perks they get, out of feeling those others are a threat to take their position.
Not to necessarily be related to affirmative action, though it kinda can be. And while not necessarily tokenism, one nigga syndrome is also in effect when whites will bring aboard one Black person into the group and cap it there so that in case he gets out of hand, he won't have backup when they collude against him.
One nigga syndrome was in effect on all but two seasons of The Real World. Notice how the token Black also tends to be gay.