No, I'd never take the piss like that..... not even out of gingers.
(BTW: Quality piss taking is expected in the UK, to the extent a US HR department would probably have a fit, and probably the moderators of this US dominated forum for the above joke!)
I would, although as with everything it's context dependent. My boss is African and has on more than one occasion got my name mixed up with another colleague (we're white). In a meeting he did it again, realised his mistake and was on the verge of saying something but caught himself. I offered in mock outrage - "Well, all white people look alike - is that it?" to which he burst out laughing as that was exactly what he was going to say. But that kind of humour (whether it's funny or not) is not at anyone's expense. It also took place between colleagues who have worked together for years now and in a setting we're reasonably sure no-one is going to take offence.