I have caught fish like this one myself on numerous occasions. These darker colored fish with somewhat of a yellow belly are always caught in the summer, in shallow water, around vegetation. It has always been my opinion that these fish take on this coloration because of the sun, spending most of their time in shallow water, and I think living in and around this shallow vegitation must have something to do with it. Someone will surely have a more exact biological answer.
I would tend to agree, those dark yellow bellied LMB are usually also hiding in the dark shade of heavy vegetation just before being caught, I suspect it is because they have been in the shade for quite a while.
I have also caught LMB on with very orange fin coloring as well which I would atribute more to something in their diet.
