Thanks! I didn't mean for him to match the rock, I didn't even know he was a marble until he started to change. Actually I posted in a betta forum because I was worried something was wrong LOL
I really do want to figure out a different plant to put in both my betta tanks instead of just the rotala roundtifolia (finally found the name).
He tries to hang out at the top in the plants where they bunch up, so I can tell he would like something else.