It's a sign of stress. So the short answer is, " yes and no." Yes, because something is causing stress, and it needs to be figured out, because long term, left unresolved, can contribute to fatalities. No. Because sometimes they just turn that color because they want to. Or maybe he's just trying to absorb some more heat. But either way, as I already mentioned, he needs a lot more foliage. This will his stress dramatically, and is the best place to start. Also, of he is new to you, try to give him a couple weeks to adjust. It takes time, and more foliage will also help in that department, too. It will also help retain humidity for him, which is another stressor. And try not to hang around the cage much. They don't like being watched. Especially when they are still adjusting. So start with some more plants, and go from there. Good luck!