Gray Tree Frog (Hyla versicolor), photo by Wrobel Photographic Arts

Paul Wrobel writes

These little guys change colors depending on their surroundings and the temperature. Here he is just starting to change from gray to green. This is a full grown adult about two inches in length. With legs extended he is about 5-6 inches long.

Our good friends at the UM Animal Diversity Web have more information about the Gray Treefrog (including pictures and sounds).