Some things matter a great deal when fish are in a selective feeding mode. Silouette and size being the most important. Generally I think the more impressionistic patterns are more effective overall. Many times fish are not in a selective feeding situation and that is when attractor patterns shine. Color is probably the least important factor in dry fly design. Fish see all dry flies in back lighting. There are no light sources in the bottom of a trout stream. Hold a fly up to the light and see it the way a fish will. You will barely be able to tell what color the fly is, subtle shades of color are meaningful only to the tyer. Of course tyers are obsessed with color because it is fairly easy to control and it is much more important to fish if the fly is a sub surface imitation.

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Ron M