How does color emerge?

The atomist maintains that when the banana goes from being green to being yellow, the only change that occurs in the banana itself is a change in the arrangement of atoms and their impact on the sense organs. Neither the greenness nor the yellowness we see is really there in the banana in the first place, but only in the conscious experience of the perceiver. … But in fact this neither reduces qualitative change to local motion nor eliminates it, but merely relocates it. For example, the qualitative change from green to yellow is now, in effect, located in the conscious perceiver himself rather than in the banana. It is a transition from the perceiver’s experiencing greenish qualia to his experiencing yellowish qualia. (Edward Feser, Aristotle's Revenge, p. 210)

Why do we see color? As explained by science, light waves of certain wavelength (in the visible light spectrum) have certain colors. In the object being seen, some light is absorbed by the surface of that object due to the photons with that energy level being absorbed by electrons in the atoms in the molecules on an area on the surface of the object. The light waves that are not absorbed are reflected from the object, and the wavelength of these light waves have a certain color. When we observe that object with our eyes, the light waves reflected from the object enter our eyes and our minds read the color of the object from the wavelength of light that has entered our eyes.

The reason why I have briefly gone through the science of optics here is to correct what seems to be confusion on the part of Edward Feser. Contrary to Feser, color changes are not changes in the perceiver only. In the case of a banana being ripened, the cells of the banana have ripened, and this ripening came about through a cascading set of chemical changes within the banana cell. Part of this ripening process is the changing of molecules on the surface of the banana, causing the electrons of the atoms in the molecules on the surface of the banana to start reflecting yellow light and not green light. Certainly, in the philosophy of mind, the question of how the color is translated into what we know as "green" and "yellow" is asked, but that is not the issue in question here.

When it comes to secondary qualities like color, the term "secondary" is not synonymous with "imaginary" or "false" or "not real." Rather, the term "secondary" means that these qualities are derived qualities that come into being due to the interaction of objects with subjects. It is subjective in that sense. For imagine if an alien organism has the ability to see infrared radiation as well, the banana would not appear to that organism purely "green" or purely "yellow," but probably tinted with shades of red. Since for that alien organism the banana does not appear "green" or "yellow," does it mean that the banana suddenly lose its "attribute" of being "green" or "yellow"? The asking of this question should manifest to us why color is said to be a secondary quality not a primary quality. Or take another example in a spaceship that is travelling at a significant fraction of the speed of light. All incoming light at the front of the spaceship would be blue-shifted. At a certain speed, anyone looking out of the front of that spaceship would see infrared radiation as visible light. Do these celestial bodies in front of the spaceship change their color "attribute" at all? Again, the question itself make no sense since it ignores how color is perceived in subjects.

In science therefore, to state something is a secondary quality is not to say these things do not truly exist except in the mind. All secondary qualities do exist, but they are emergent qualities not fundamental qualities. Feser should really brush up on his science, because not understanding science is undermining his case.