Hi Matt,Interesting. The duns I see are lighter-bodied and have speckled wings, but I've never seen speckled wings on a spinner, and the spinners are always dark-bodied.
Unfortunately, I don't have Callibaetis pictures from Dry Falls. But here are some dun and spinner pictures from Leech Lake - much darker in the duns.
Duns
Spinners
This next spinner does have some color on the leading edge of its wings.
Steve