I would guess he is a bit stressed is all. You also have dark substrate which will keep him.a bit darker.
I suggest using something to block some of the light overhead. Fish generally don't like being in direct light even more so when young.
Add some more caves and such for hiding. He likely won't use them very much but he will like the idea of knowing they are there.
Who else is in the tank? What size tank? What temp are you keeping the tank at?