I'd say it is just becasue of its surroundings. I know with my saltwater natives, if I catch them right then, they have darker colors and patterns. But once I get them in my open lit tank, they become much lighter. If a bass is caught righ tout from a pond or river or wherever, it will be colored darker to blend in with its surroundings, vegetation, rocks, shade, etc..., rather than one at a store that is in an open lit tank with not as much natural enviorment . Or am I totally wrong on this one?