I don't take photos (not since film went out)so maybe this question is below standard requirements, but... I caught a BG today that was blue gray (about the color Navy planes were painted on their bellies during WWII) from the tip of its lower jaw to well back on its belly. A broad strip of this color, and it was nowhere else. I can't recall ever seeing this color on a fish before. There are RES in the pond, and I stocked GSF last fall, but this wasn't any of their colors.
My sediment pond goes from reasonably clear to turbid with rain events and runoff coming off agricultural land. When I had CNBG in that pond they would come out very lacking in color when the water was turbid. When the water was more clear they would have much more coloration.
If you want to try an experiment, find a clean black 5 gallon bucket. When you are fishing fill it a little over half with pond water. Then when you catch a BG instead of returning it to the pond put it in the bucket for several minutes. Then retrieve it and note the color difference from when you first caught it. The difference can be striking.
The color of bucket you use makes a difference. When I was transferring lots of BG from my main pond to my old pond to get BG going there because of the GSF infestation, I found the fish to be much calmer if I kept them in a black bucket while they were waiting to be transferred to the old pond. A white bucket was the worst as it seemed like the fish noticed any of my movements and thrashed around a lot more than when I stored them in a black bucket. So in the back of my 4 wheeler I always carry a black bucket in case I want to hold fish for a while.
Put a BG in a black bucket for a while, note the color as it comes out, then in a white bucket and their colors will change because of the amount of light entering the bucket. It is a quite interesting thing to try.
I see various fish changing their chromatophores (coloration) all the time in real time while scuba diving in the ocean. They do it in mating, sometimes as other fish or divers approach, as they swim past different parts of the reef, lots of different situations. Some can go from almost black to almost white (grouper good example) and some all the colors of the rainbow (file fish, trumpet fish, etc.), depending on the species.
