I've been experimenting for quite a while with the significance of fly color in "matching the hatch" situations and simply put I've found it to be almost completely irrelevant. Just this past week for example was casting to a 14 1/2 wild brown feeding selectively on sz 16 sulpher spinners....threw at him 16 sulpher parachute, 16 sulpher parachute with a thinner body, and 18 sulpher parachute...exact imitations, perfect drag-free drifts and refusal after refusal of these exact imitations...then threw on a cdc rusted brown/light brown spiral comparadun and this selectively feeding wild trout gobbles it greedily after close inspection...missed him on the set and subsequently caught the tree behind me losing that fly...tie on a cdc mosquito comparadun (black and white spiraled)...give the fish 5 minutes before casting to him again...and once again readily took after inspection however this time stuck him on the set and brought the 14 1/2in wild brown to hand. This is a heavily pressured river..in the most heavily pressured pool on that river...casting to a streamborn nice sized wild trout feeding selectively on 16 sulpher spinners whom after repeated refusals on exact imitations in parachute, I got to take two separate CDC comparaduns in colors far from the distinctive "sulpher yellow" in slow moving water after scrutinization...and again this is just one of a plethora of times where this exact same situation has occured. Comparadun has a closer resemblence to a spinner as it rides a little lower than a parachute which is what I feel made the difference, but fly color has consistently been almost entirely insignificant. I say almost entirely because if I were throwing lets say a bright pink colored CDC Comparadun to "match the hatch" as opposed to a tan or gray then maybe there would be a bit of varience as the color is so completely outlandish and gaudy in comparison to what you're attempting to "match" that it could be potentially off-putting. Size, Shape, Stage of emergence, and most importantly a smooth, accurate, drag-free presentation are what truly matters when throwing dries...color on the other hand, as long as it's not something completely ridiculous, is of little to no substantive value and really has more to do with personal security on behalf of the angler than it does on behalf of the fish. Long story short if an angler has the Size, Shape, Stage of Emergence, and Presentation correct you will still be productive even when throwing a "wrong colored" adams pattern during an olives hatch...furthermore the last time I looked at the underside of an actual Light Cahill mayfly I didn't see a size 12 brown hook jutting out of it's abdomen, which any slow water scrutinizing trout undoubtedly sees in the counterfeit version, yet still chooses to take the fly anyway despite this blatant "flaw in cosmetics"...feel free to weigh-in.