when one asks about colour, is it what colour or which colour?
could it be 'which color is a XXX' ?
It could be, Marcio, but what the XXX is might make a difference.
which colors can a man [can] be? it means... what's your skin color...
If you were displaying a number of clors, 'which' could be used, but an open-ended question would tend to use 'what'.
what colors can a banana [can] be? so, could one say: A banana is yellow, but it can be green if it's not ready to be eaten.
Yes, this is kind of an open ended question, even though there are limited choices.
Are both right?