Sometimes you simply have to handle a frog, like to move them, to examine them, and when it's necessary to medicate them. Purchase some blue nitrile powder & latex free examination gloves, or the clear kind they use at deli counters. I wouldn't use the deli cup because these guys are all legs and jumpy (especially if he's full sized) so you could risk damaging his eyes or limbs even if you are careful. Cupping him in your two hands gently is safer & faster.

Quite frankly it sounds to me like you're spot on with everything. If he's active (without being crazy trying to escape), and certainly if he's eating and calling, these are all good signs. I don't know about how often RETFs change to dark, but I know White's tree frogs change color all the time, and it doesn't always mean something is wrong. I have a frog who is pale blue-green when she sleeps during the day, and at night she turns a dark purply-grey color. I have another who is chocolate brown all day long but when the lights go out he turns olive green. Another frog, who is usually a nondescript green, turns brown day or night seemingly when she is ticked off... lol. But Martha is a grump, so...

Sounds like you are on the right track. Keep an eye on him and come to learn what is "normal" for him as time goes on... if activity, eating (remember to dust those feeders with Cal/D3 and mutli vits once a week on opposite days!), poop, soaking, & shedding are all happening and he's not just all hunched up looking miserable and refusing food things should be fine. It would be a good idea to grab a fresh poo and have it tested for parasites too. The thing about this is fresher is better, so I'd see if you can find a vet office that can do this in-house instead of sending out to a lab-- IF they will do it without seeing the frog, which can be tricky. You do not want to have to haul an otherwise normal frog in to a vet just to have a poop test run... if it comes back positive for something you might not have a choice, so you can get meds, but a good vet will let you birng in a photo or video of the frog, imo.

You can look up Dr. Frye on here too, I believe he does fecal tests through the mail? (anyone?) but again the fresher the better as it helps prevent false negatives.

Keep us updated on Gru!