Hey Dave,
Alot of panther chams have a yellow mouth...mine unfortunatley was something to worry about though.
My chams mouth was yellow and I thought it was nothing until she started going downhill. Turns out her mouth was johndis, and it was related to her liver.
If you notice any changes in your cham..lethargy, not eating, drinking, or dehydration, don't think twice pack up and get to the vet just to be on the safe side. It may cost you a bit of cash but to not be worried about it's health would be worth in IMO.