And yes, it is a frog! Which is good, because, as I said to Brian during an email exchange in which we were puzzling over the animal's identity, "Toadma" just doesn't work as well as "frogma".
Anyways - it seemed like everybody was baffled on this one, so this morning, I passed the question on to my birder friend Prof. M (aka "She Who Produces Snowy Owls Upon Request", I'm still amazed that she found us one of those). She passed it on to a few friends of hers & by this afternoon, one of her friends had sent this message:
Note the following about coloration of the Gray Tree Frog, Hyla versicolor....//S.
Introduction: Gray tree frogs are medium-sized tree frogs native to eastern North America. They are common in much of their range near small bodies of water, and are often encountered by humans during the breeding season in spring. If you capture one in the wild and keep it in captivity, do not release it. There are two species of gray tree frog: Hyla chrysoscelis and Hyla versicolor, both of which look identical and can only easily be told apart by their call. In captivity they both require the same care. Adults reach a size of around 2 inches (5 cm). As their common name suggests, most are predominantly gray, although their ventral side is a light white, and on the inside of their hind legs there are two bright orange or yellow flash marks. Gray tree frogs have the ability to change color depending on temperature, humidity, light intensity, and the color of their surroundings. They can range from bright green, to pale white, to dark brown, although most of the time they remain gray. Juveniles are generally green in color and develop their gray adult coloration as they mature.
[Not sure if you’ll be able to open the link below – if not, google gray tree frog + green and the image will show up on the top row]
I was indeed unable to open the link, but I followed her instructions & sure enough, there was Mystery Frog's twin!
The picture was posted on the Amphibian Care section of the Reptile Forum UK - hence, I think, the warning about not releasing them, the poster was concerned about erstwhile herp fanciers creating Yet Another Invasive Species Problem, as he was addressing people who live in an area where the Gray Tree Frog is not an endemic species, but would probably like things just fine, thank you very much (cf: Gray Squirrels).
Thanks for the I.D., S., I never would've figured that one out on my own!