Much as the phrase '
that's Catholic of you,' this phrase can be a bit of a holdover from a much less
tolerant time. In many parts of the world, the
Black was an image of
selfish savagery, and the white an image of a
benevolent,
paternal master.
Caucasians abroad would use this phrase to indicate that the person being addressed had proven their superiority to the natives by exhibiting 'good' qualities of character.
I do understand that this phrase is used many times a day without anyone consciously attaching racist motives to it. However, I think it behooves everyone to at least be aware of the history behind the phrase, if for no other reason, it might save you a serious spot of trouble if you would have otherwise used it in the wrong company.
On a more normative bent, I would ask everyone to think carefully about this phrase and how and why it's used. Sure, I understand that some folks might fiercely disagree, stating that 'white=good' and 'black=evil' predate the American slave trade and British imperialism. That's true. However, remember; it's not your interpretation of the phrase that's at issue here, nor your intent when using it. It's the interpretation of everyone who is in earshot or hearsay when you use it. You can argue that it's PC to worry about everyone's feelings. Note carefully I'm not telling you not to use it. I'm asking you to be aware of its connotations when you do use it; it might explain why you just got your ass kicked for, as far as you could otherwise tell, no reason.
Of course, you might consider not using it at all.