A new revised copy with new flies and illustrations by Dave Whitlock has been in process for a couple of years. The key to identifying mayflies is the upright wing. Looking at the wing closely, it resembles a stained glass window. Mayfly drawing from The Mayflies, or Ephemeroptera of Illinois by B.D.Burks. Opaque is freshly hatched.
Shiny wings means the bug is ready to lay it's eggs.
That is usually in the evening unless it is a dark overcast day. So you do need to look at the wing color. To that observation, add the color of the body, and if the insect has a tail or maybe two, or three. Almost like an airplane on the water. For the best success, you really do need to match the hatch.