...because some dragonflies change color when they die, so depending on how long it had been dead, the color you see there may not be the color it wore in life. There are some clues you might have seen that the photograph doesn't show...the sides of the thorax (the "body"), whether plain or patterned. The color of the face (front of the head), eyes, underside of abdomen. (The Common Green Darner, which looks as if it has a green thorax and blue abdomen from the side, seems to have a brown abdomen from above...this could be that insect, if the green color is the same as in life, and the underside and sides of the abdomen were blue.) The length and the wingspan.

The real dragonfly experts here may know, of course. I'm just an appreciative amateur.

Have you looked through the dragonfly pages here? You can search by clicking on the dragonfly icon (among the other insect shapes in the column on the left hand side of the page) or by entering "dragonfly" as a search term.