There is little doubt that contrasting "color spots" can play a role in the "eat/ don't eat" matrix. (Insert color of choice here)-butted flies and lures have been a thing since folks have been tying flies, and the same is true for folks putting red for "gills". While there is some merit to the practice (in the form of contrasting colors), I would say the other factors in your assessment (most notably profile and size, IMO) are WAAAAY more important to successful fly design than the "bin appeal" of gills and eyes. Try a few different colors of gills besides red (chartreuse is one of my faves) and see what happens - you might be pleasantly suprised.