Grey treefrogs are Hyla versicolor, BTW. At least last time I knew. I found out they re-did the naming of some snakes and cornsnakes are no longer Elaphe(I can understand this as people have crossed them with kingsnakes, milksnakes and pinesnakes).
There are albino green treefrogs, so I don't see why a grey would not arise. Keep in mind, almost everything produces occasional albinos, but it's not best for them, as they sit out like a sore thumb and usually get killed wuickly in Nature. Leucistic(sp?) is a white form, with normal eyes. If this one is so light that is would stick out, you may want to keep it as a pet, as it may be doomed in the wild.
A half water/half land detup would be good for some of these, with small insect food available(maybe fruit flies if the froglets are small enough).