Now, I think this applies to conventional anglers as well as fly anglers but possibly more so to us...again and again you can hear, read articles or see videos where people assert with absolute confidence that the fish is taking a fly/lure because it imitates X prey species. Fair enough you might say, and I'd be inclined to agree in certain situations. For example, catch a midge feeding trout on a midge pattern that is the same size and colour as the naturals and you can reasonably assume that the fish "believed" the fly was a midge. But the tendency is, to my mind, over applied. Do daphnia feeders really think fire orange blob is a giant clump of daphnia? How about great lakes musky eating a firetiger baitfish? Or do smallmouth really think a boogle bug is a giant insect? It's impossible to truly know but I'm skeptical.
It might not seem that important and may even be an advantage at times as far as confidence goes, but I also wonder if it can be an impediment to our when imitation is important. As an illustration on a recent smallmouth trip I tied on a bucktail deceiver about 7 inches long with an olive back and a bit of yellow near the head, because I suspected that the big post spawn females would be feeding on ayu. I caught a few fish including a couple of 20 ichers. A local I met was struggling to get a pull but couldn't understand why his pink "baitfish" wasn't eliciting a positive response.
There are of course situations where a non imitative fly is the killer pattern when fished correctly, but even then many of us desire to claim imitation. In Harry Murray's excellent book he includes the dressing for the James Wood bucktail, a simple but very effective fly for bass. He asserts that bass eat it as a small sunfish, one look at the blue and yellow fiasco and you'll surely agree that this is quite a leap of thought. But the fly really works and if telling yourself that it's a baby bluegill helps then maybe that's enough.
Personally I like to tie them in olive and browns which I know get eaten for dragonfly nymphs ;)
James Wood bucktail dressing:
Hook: 2x long nymph hook 6-10
Weight: lead wire (optional)
Rear 2/3: yellow chenille
Wing: White bucktail tied roundthe shank
Front 1/3: blue chenille