I'm not sure how, but it knew!
While checking out the breeding Luna Moths on my son's window this morning, we noticed this Gray Treefrog as well. They can be a range of colors from Gray to Green, and combinations of various shades of them, but somehow, it seemed to be exactly what color our house is! Check this out. It should work in the paint department of the local hardware store or something. What a color-match... wouldn't you say?
COLOR-MATCH TREEFROG PHOTOS