Question

I read in a book — not in its main field, just as an aside — that since colors are specific wavelengths of light picked up by the eye, and since there are lots of things that affect wavelength (the angle of the light source, heat, etc.), the eye should really perceive different shades each time in the same object. But the brain makes “corrections” to what the eye sends it based on what it expects to see. Is that really so? I don’t know whether the way I described it fully matches what was written in the book; in any case, that’s what I understood.
What interests me is the practical implication for examining blood appearances and skin afflictions, and the like: if that is indeed the case, it turns out that my expectations have a major effect on what I will see and what I will rule.
I’d be glad for a physics-oriented opinion on the subject. Thanks!