It is my understanding....ok, ok, I just read that while it is common for goldfish to change color, sometimes this can be a sign of trouble. For example, if the fish is turning a more bland color, it could be a parasite that is infecting the fish. The example given regarding a turn towards white was that a "silvery" white might be 'normal' to expect in some fish but a turn towards 'albino' white could be a parasite or if the 'albino' color is limited to small patches, perhaps a fungus. As far as I know, fish aren't exactly photosynthetic and based upon that understanding, why wouldn't adding more light result in more colorful fish?
P.S. If you haven't already Greg, please check your PMs as I sent you a reply a few days ago.