I don't know what it is, but the rays of crowntails do seem to change as they mature. A few months ago I won a black and white butterfly ct with white on the outer half of all his rays. He was gorgeous! Then, just before the ship date, the seller sent me an updated picture of him and asked if I still wanted him....he had turned completely black! No white on his rays at all. I wish all sellers would do that....especially with the marbles! Some I've bought have been totally unrecognizable by the time I received them....I had to identify them by the process of elimination, matching up any other fish with their pictures until I knew who the "mystery" fish was.
Currently over 100 males and females (mostly from Aquabid)....and I have now completely (almost) sworn off Aquabid...lol....waaayyy too addictive!