Just as saidin seems to bring up the "taint" of the Dark One, I think that the colors that the ta'veren see are associated with the Creator. Everything in these books has an opposite, so the opposite of the taint must be the colors. Just as the Dark One can look in on what's happening in the world, so can the Creator. I think that's what the Creator must be doing whenever the three ta'veren think about one another. It would be interesting to see what happens with those colors if the boys continue to think about one another for more than a few seconds...