To become skilled and successful at fishing dry mayfly imitations the angler must come to understand the behavior of the trout and how the trout will react to any number of natural and unnatural situations that are encountered.
I would argue that much of the time, a trout doesn’t see any color at all.
Hold a fly up to a light source - no color; the fly looks black.
Depending on whether or not the sun is out, and its position, we could successfully fish a bright orange fly during a Baetis hatch as long as the size and shape were correct.