latge mouth bass

So I have 2 LMB around 5 inches, healthy, good eaters that I have had for around 3 weeks now. The one is colored up fine but the other has been almost black the whole time showing no markings. I do not know if this is normal or not, they swim around usually together but their behavior is fine just confused on the coloring, any input would be great, thanks. Oh by the way they are in a 180 gallon with somewhat heavy plants and filtration for up to 400 gallons.

Was there that much difference in the color of each fish when you caught them and did they come from the same place?

yes same pond, and similar color, though the one was a little darker. I will get some pics up tomorrow.

The amount of light reaching the fish can have an effect on the degree/intensity of color. Could also be difference in each fish's dealing with stress of adjustment as stress, excitement, fear, aggression, etc... can cause a color change. Could also be just a natural difference in each fish. I've got 2 rock bass that are the same age and came from the same place on the same day a couple of years ago. They live separately, each the top fish of a tank with plenty of hiding places. One of them stays light grey, the other stays very dark. Each can still change to look more like the other, they just happen to "prefer" a certain way. I've had them both in dilfferent tanks in a variety of set ups, and while they may change momentarily, they will always return to their preferred color. On another interesting note about these two fish; One of them comes to the front of the tank to meet me, eagerly awaiting food, while the other one has never been able to make the connection between me and food. While it's not terribly afraid of me, it obviously has never realized that my presence has anything to do with food. Just like people, every fish we pull from the water is different and unique in it's own ways.

I have two brown bullhead in a tank, the one that spends its time in the open has a greyish color and narrow fins, the ones who spends its time hiding in the stump decoration is black and has large, full flowing fins.

well the dark one lightened up a little and has gone back to almost all black, he comes out of hiding swims with the other and eats readily. so I will assume then it means nothing i was not sure if maybe it had something to do with sex or not.

Could this be a male/female exchange or maybe a dominance thing? The dark one swims up to the other and bumps and nudges with his head to the under side of the other, he also swims up and it looks as though he is biting but really is just like rubbing his mouth on the other, it does not look aggressive nor does the other seem to take it that way.

I could be wrong, but I'm guessing it's a dominance thing. This sound just like what my SMB has done with any kind of fish that I've tried to make live with it. With the smallie, the darkness/intensity of the markings is directly related to the amount of aggression/excitement of the fish.