These are darker colors on a pair who aren't really happy with each other. When one fish enters another fish's territory, the landowner gets nasty with the other, chasing it, cornering it, and mercilessly biting at it's side. When they are "tolerating" each other or hiding from each other they wear their darkest colors. In this case, the front fish is the dominant fish, but he has scrape marks on his side from previous mating battles.