I think they are almost out of colors already. I doubt they'll do Orange, Purple, Pink, Brown or Grey. None of those have a good counterpart, and some of them are just boring. I would expect the third game of the fifth generation to be something like Rainbow or Spectrum rather than Grey.
Even though some people are saying "lol dere iz milyuns of colours," we're talking about naming conventions here, not distinct shades viable to the eye. So there really isn't too many options left. Ruby and Sapphire was already like re-using Red and Blue, so I doubt they'll use Crimson or Topaz or Cobalt or whatever. Ultraviolet and Infrared at least is a decent idea.
But in general, I think it makes more sense to stay basic or elemental than to just use more and more colors. Sun/Moon would be better than Mauve/Periwinkle.
"[Our former customers] are unable to find software which they WANT to play."
"The way to solve this problem lies in how to communicate what kind of games [they CAN play]."
Satoru Iwata, Nintendo President. Only slightly paraphrased.
