None of these are straight-forward “linear” sums: there are differing amounts of each type of cone cell in the retina (and the proportions vary from one part of the retina to another), there are several levels of combination of signals which we don’t fully understand currently, the eye/brain adapts to what it’s just been looking at, what else is in the visual field, what it knows the light source to be, what “memory colors” it expects for an object, and so forth.
Thinking of the mechanisms of the eye operating directly on “FFFFFF” is a very imprecise model for what’s happening.
Thinking of the mechanisms of the eye operating directly on “FFFFFF” is a very imprecise model for what’s happening.