There is a couple ways of looking at this. The first is that size is critical. In most cases your probably better off matching the size of the flies on the water. If in doubt about the size its usually best to error on the small size. The second is the color/shape. And last is the name. I fish a "Flav" hatch on the Poudre that always seems to match better with Blue or Grey Quill Dun than the small Green Drake its suppose to look like. I now this seems elementry, but if your size and color match whats on the water the fish sure does not care if it has the right name.

A.K. has even developed patterns in this vein. For example his Frying Pan PMD is pinkish in color. Are PMD's suppose to be pinkish? No, but on the Frying Pan thay are. Okay lets do a quick review:

1. Match size first.
2. Match shape next.
3. Match color last.

Of course thats just my opinion.