All of the important mayflys in Mo. are cream, or very light olive.
Hendrickson's, Red Quills, and Brown Drake's exist.... but they have no FISHING importance here. Learning about those bugs is fun, but don't let it slow down your angling learning curve, because THESE trout don't care. Ants and beetles are usually more important than Mayflys and Caddis.
One minor exception....the Current has Trico's