Dark black Bolivian ram?

I got 3 Bolivian rams a couple days ago, and they settled in decently, although it’s rather difficult to sex them. One particular ram looks to be the dominant one in the tank, and chases both of the others out of its territory. Tonight, however, I noticed it had gotten really dark. It darkened first out of the three, making me believe that it was simply better adjusted, but the upper half of the fish is almost jet black.

Any ideas? He’s eating fine and acting reasonable. All the other fish in the tank are great.

Nevermind it turns out it was guarding eggs on that leaf.