Few days back I read an excellent article, titled "The Science of Avatar". It is a great analysis of the movie from scientific point of view. If you liked the movie, you should check out the article.
In that article, the author explained the meaning of colors in a way that I never had imagined before. Here is the quote:
In fact, colors are really something manufactured in our brain -- physically colors are just different wavelengths of light ranging uniformly from short wavelengths (violet) to long (red). What we see as blue or green or red helps us differentiate sky from grass from blood, but to a creature from another world, all these things might appear as the same color. In fact, you could imagine that bats might use echolocation to "see" rough surfaces as one color and smooth surfaces as another. So since colors are something created by our brains and not intrinsic to the universe (only wavelengths of light are), it is virtually certain Pandorans would see color differently than we do.
So there is no Red, no Green, no Blue. It only exists in our brain. Wow! We already live in a Matrix. A simulation which gives us joy by interpreting different wavelength lights in different ways. So if some alien race tommorrow finds our artwork, they might as well see blank slates.