I am guessing it is in the breeding lines of the fish. I have 6 labs right now, and they are 3 males to 3 females. Some of them are bright brilliant colors, and some are starting to show the grayish/brown colors on the laterial lines. I will end up getting rid of those ones and keeping the bright colorfull ones. It is just a thing you get with labs. So if you want a colorfull one pull that fish out and go get some more, and hopefully you will get a colorfull one.