They can change their coloring depending on mood, lighting, etc. Mine shows anywhere from a light honey tan coloring all the way to almost jet black depending on mood.
I've seen it work, but I haven't tried it personally. I doubt mine would allow for it unless he was in an exceptionally large tank with room for others to get away.
I have done it. I had two, one was and is very fish aggressive and can't be kept with anything. The other I mixed with various fish, only issues were similar shaped fish that shared the same territory. This was in both a 6' and 8' tank, I personally would try it in anything smaller than a 180