Hyla versicolor or H. chrysoscelis
About 1.5 inches long, with mottled gray skin. According to the Virginia Herpetological Society, H. versicolor and H. chrysoscelis are indistinguishable in the field except by their call (which I did not hear).
Forages in trees and shrubs near standing water.
Both gray treefrog species are known from Chesterfield County, Virginia. VHS says that H. chrysoscelis is usually not seen before May, but this is not enough to make a positive ID on my spotting.