A suburban moral code, to be "white about it" means doing things the way white people do it, this includes being truthful, sticking to your word, being on-time etc..
When in mixed company telling someone to "be white about it" often leads to PC types jaw dropping and much offense taken.
White suburban dude #1: Dude, can I borrow twenty bucks for the bar? I don't have any cash.
White suburban dude #2: That's cool, just be white about it and pay me back.