The Black American Express card was one of those urban legends that became real:
http://www.snopes.com/business/bank/blackcard.asp
Based on this article, AMEX didn't 'keep it real' for too long. As others on this board would say: "He's dead, Jim."
However, you have to hand it to AMEX. As the Snopes article mentions, they tried to capitalize on an urban legend instead of being the victim of it.