This is my first theory, go easy! Okay, I think the colors that Rand, Mat and Perrin are seeing is something similar to the longing that Ogier feel when away from a stedding to long. The Three main characters haven't been together in quite some time and the colors only appear when one of them thinks of one of the other two, or more to the point, Rand, it was commonly stated he was always pulling Mat and Perrin towards him, and this could just be another way no doubt the last battle will be very soon, and the need of all three combined very great.