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Ashley is correct. It is a newly metamorphosed grey treefrog. They are green when they first emerge from the water. It is not a green treefrog.
This is definitely not a Green Tree Frog, it doesn't have any of the characteristics of one. And Guy Bird's suggestion is also not correct. Like I said in my earlier comment, they is no way to tell them apart by a picture, and both are in range, so you cannot call it either one of the species definitively. You can only say it is one or the other.
It's a little out of it's mapped range, but this looks like a green treefrog - Hyla cinerea. Check it out at http://www.npwrc.usgs.gov/resource/herps...
These two species are visually indistinguishable and are both in range, so at this point you cannot tell which species it is.