1. None of the photos in my references depict a thorax with such small dark areas, at least in a species known in my area (unless pruinose, covered in the white powdery bloom that develops as a male ages).

2. The shape of the paraprocts, the lower appendages at the end of the abdomen, could ID the species, but they seem to be missing here.

One clue: a reference mentioned that in several species, the dark part of abdomen may be green when immature. I do see a hint of green in the abdomen and the dark patches on the thorax. Could this be a very young adult who hasn't yet developed his bloom?

Magnuson Park, Seattle, Washington State, August 25, 2015, on a path through an artificial wetland.