Wikipedia says:
Play the white man is a term used in parts of England meaning to be decent and trustworthy in one's actions.[citation needed]
The origin of the phrase is obscure. The term carries with it a reference to an obligation which many English civil administrators in the latter years of the British Empire might have considered themselves to be under: that is, the obligation to uphold respect for their county abroad by maintaining personal standards of behaviour and fairness which darker-skinned native peoples could respect[citation needed]. The act of calling upon someone to remember his personal moral obligations in this way is expressed in Rudyard Kipling's poem The White Man's Burden. On the other hand, the racially neutral colour white has long been associated with pureness and virtue.
A similar expression in the United States is "That's mighty white of you", meaning, "Thank you for being fair". Among African Americans, this phrase is said in response to being patronized or told what to think.[1] [2]
It is also widely believed that the term 'Play the white man' comes from the days of black and white movies where, to differentiate between the groups of people, they put the 'goodies' in white and the 'baddies' in black - it had no relationship to the colour of their skins.
That is what I thought it meant ... not racist at all