Play the white man
From The Art and Popular Culture Encyclopedia
Play the white man is a term used in parts of England meaning to be decent and trustworthy in one's actions. The term is considered by some to be derogatory against non-white people because they believe it carries the implication that only caucasians are decent and trustworthy. Originating in colonial England, the term is losing popularity in common parlance.
A similar expression in the United States is "That's mighty white of you", meaning, "Thank you for being fair".
The term "play", in African American slang, can mean "cheat" or "swindle", and "the white man" is often a reference by minorities for the perceived historical collective oppression by Caucasians of non-Caucasians. Thus if used by non-whites, the term "play the white man" may carry a connotation of "cheat the oppressor".