Hey there....this just caught my eye....The dark brown coloration can be a sign of stress and/or of low temperatures. Your cham is under stress since you just got him and he has not had time to adjust. I'm also going to suggest that you bump the heat at the top of the cage up. The bottom of the cage should not be lower than 70 degrees and I would put another basking light on top of the cage (raised above it so he can't get burned) to raise his high cage tempurature to 95 degrees.
Panther chams need warmer temperatures than Veileds do. Chams under stress or that are ill need much higher temperatures too. They rely on this heat to keep their metabolism up. I always keep my Panthers at 95 degrees at the upper area during the day with a light producing basking bulb. During this time of year a night heat bulb (red, black or ceramic) stays on all night. During the summer I turn them off. Your cham will regulate his temperature by moving in the cage to the proper level. I really don't think that 85 degrees at the top is warm enough during this transition/adjustment stage. He could easily get a respiratory infection. If you see him with his mouth gaping open you know the temperatures are too high. Well adjusted healthy adult Panthers may do fine with 85 degrees as a top basking temperature. But if they ever showed any sign of illness of improper food digestion the temperature should be increased. As I said, I always have 95 degrees available to my Panthers. They spend most of the morning and afternoon there and then move down later....Let us know how he does as he adjusts