We were excited when Capitan the superintendent of the building next door and member of Friends of Brook Park pointed out a small friend in the garden!
As the scientific name implies, Gray treefrogs are variable in color owing to their ability to camouflage themselves from gray to green, depending on the substrate they are sitting on. The degree of mottling varies. They can change from nearly black to nearly white. They change color at a slower rate than a chameleon. They get to be about two inches long, live mostly in the trees and can withstand below freezing temperatures!
It is the Gray Tree Frog, also known as the North American Tree Frog. See the distribution map here.
Here is a video of the call: