A person of color, especially a black person who acts in a way so as to come across as trying to please or gain approval of the white-dominated establishment. Example of folks in the recent past accused of "Uncle Tom" behavior are Condoleezza Rice, Herman Cain, Allen West, Artur Davis, Angela McGlowan, Michelle Malkin (née Maglalang)
Mitt: Did you hear what Condi said about Obama?
Ryan: What what tell me?
Mitt: She said I'll be a much better world leader than Obama since I understand American exceptionalism.
Ryan: Love it. Gotta love them Uncle Tom wannabe's. They just so want to get our approval.