lost his color?

[Cholbert]

i have a cichlid tank with 2 labs 1 acei 1ngara 2 peacock and a pleco in it. today when i got up to feed them i noticed that one of my labs now has no black on his fins. he did a couple days ago when i was watching them. the other lab has lots of black and they looked the same. now one is all yellow. is somthing wrong with him or he just lose dominance ( spelling ). thought they were both male. no strange behavior at all. just lost his black lol