The knowledgeable staff at the Wachusett Meadow Audubon clarified the types of frogs I had photographed there:
The brownish frog here is actually a Green Frog, distinguished by 2 ridges that run from behind each eye to its back legs. The frog that is mostly green is the American Bullfrog, and he will likely get much larger. Both species often share the same habitat (permanent water). Learn more about the 10 species of frogs found in Massachusetts:
http://www.massaudubon.org/learn/nature-wildlife/reptiles-amphibians/frogs/frog-species-in-massachusetts