I added 2 juvenile yellow watchman gobies several months ago. Both gobies were bright yellow, and about 3/4” when I got them. One of the gobies have dulled off quite a bit, and has been getting blackish strips, and seems to be developing a black mustache. It’s just pigment, not actuall facial hair. He hangs out with the blood shrimp when the pistol doesn’t want to come out. Sometimes both of them. The pistol doesn’t mind the blood as long as there’s no food around. The other goby is living by itself, with no shrimp. The second goby has remained bright yellow. The aggression between the 2 has mellowed out, but they still don’t interact much. The one that’s darkening has alway been the dominant of the 2.