Of my 3 I have one that does this absolutely amazing colour transformation, it goes from normal tan/sandy colour to almost black with deep green/blue markings around the head. He (I say he, but I am not sure) will swim to the middle of the tank then change colour and twitch/head shake/shimmy (severum shudder if you know what I mean) with all fins extended. I am taking this as a territorial sort of display as "he" does it in the same spot. I have not seen a fish with such amazing colour transformation before, do your's do it?