According to David Louis’s book of Fascinating Facts, it is believed that this is why surgeons, watchmakers, and others who perform delicate manual operations are so bothered by uninvited noise: the sounds cause their pupils to change focus and blur their vision.
The “millions of colors” that the eye can detect are the three primary colors of red, green and blue and the millions of combinations that result from these three colors. (In 1878, Ewald Hering proposed the theory that the four unique hues of red, green, blue, and yellow form the basis of all colors.)
The eye is, of course, just a lens for the brain. You actually see with your brain.