I decided to make an account just for this thread and to clear up some misconceptions regarding waxy monkey tree frogs. During the day, waxys are able to secrete a wax like substance from their paratoid glands that they use to cover their bodies, thus forming a cocoon to protect them against the intense Gran Chaco sun rays. At night, they will remove this coating to descend from the trees for a nightly soak in water and to hunt feeder insects. If you keep this in mind for their captive care, then their physical appearance differences from day, dusk, night and dawn are not out of the ordinary, and not requiring medication.
Your frog looks healthy and either in a night or dawn coloration, hence the darkening of the pigments. Keep these guys on the dry side with clean water available at all times. I like to give mine a weekly misting, mostly for the plants of the enclosure, but the frogs enjoy it as well. Any other questions, feel free to ask. Mike Moby is the Phyllomedusa guy if you have questions in regard to breeding or husbandry.
Derek Benson