I look at grey tree frog pictures and some are green. I have about 20 mated pair of tree frogs that come every year to my pool and they are all greyish color. But I see other peoples grey tree frogs and they are green and adults. My grey tree frog was green until about 3-4 months old. My grey tree frog can change to a light grey almost white, dark grey, and light and dark brownish. He is never green. Why are some adults green?