Trout Fly Fishing and My Perception of the Reality

Studying Brown and Rainbow fry in the circulating water of a large aquarium was a good starting point to search for alternative possibilities and, hopefully, some answers to long pondered questions.
They survived initially on their yolk sacs. As soon as they had the strength to swim, each species automatically took up their classic feeding situations - Rainbows at mid water and Browns nearer the bottom. As any tiny neutrally buoyant non food item came around in the current, it was taken, mouthed and rejected. Next time around, again it is taken by the same fish, mouthed and rejected. Here it comes again, taken, mouthed and rejected.
Therein is the Trout's initial basic blueprint for survival. Anything which comes along and is small enough to fit in the mouth is taken. If the fry considers it feels or tastes wrong, it is rejected. If it could be food, it is swallowed.
Some of what it swallows is not food. It seemed that if they couldn't reject it with conviction, they swallowed it in hope. This habit stays with the Trout for some time and we see things taken like gum nuts or seeds the rough size and shape of beetles, for example. Enough of what is swallowed is ingestible to sustain life.
This basic process has to be repeated thousands of times. During this repetitive process, the Trout would have to start to recognize different features which signal a greater likelihood of an item being edible. I have labelled these features 'Recognition Keys.'
While our traditional angler pores over coloured plates of the different insects, the Trout has no such luxury. A Trout's view of insects on the surface could be broken by reflection on the under side of the surface. They might be dishevelled, water logged, tumbling, obscured in discoloured water, or any combination of these factors.
'Recognition Keys,' however, can make food items readily recognisable for the Trout.
Dual or multiple colours, for example, particularly contrasting colours could be picked up at a glance, irrespective of the conditions.
If you use an underwater viewing scope, you will notice that most immersed mineral and vegetable group items are a single drab colour. Try to think of any small dual or multi coloured buoyant item which would not belong to the 'Animal' group. Nothing obvious springs to mind for me.
It should not take too long for a Trout to start to associate multiple colours, or shades, on a single item as usually constituting something edible. So multi colours becomes an obvious 'Recognition Key.'
Next chapter is devoted to identification of those Recognition Keys.
The relevance is that any fly tied with multiple colours automatically signals to the Trout an increased likelihood of being edible, recognizable or not. In faster water, the Trout has neither the time, or conditions to wait for absolute recognition.
In slower water, the Trout has more time but smaller flies minimise the impact of any close inspection.