There's no definition for "color" in physics. Physics does quantum electrodynamics. Chemistry then uses that to provides an abstracted mechanism for understanding molecular absorption spectra. Biology then points out that those "pigments" are present in eyes, and that they can drive nerve signals to brains.
Only once you're at the eye level does anyone start talking about "color". And yes, they define it by going back to physics and deciding on some representative spectra for "primary" colors (c.f. CIE 1931).
Point being: everything is an abstraction. Everything builds on everything else. There are no simple ideas at the top of the stack.
> There's no definition for "color" in physics.
This is unnecessarily pedantic. Your explanation demonstrates that.
> There are no simple ideas at the top of the stack.
I don't know what a "simple idea" is here, or what an abstraction is in this context. The latter has a technical meaning in computer science which is related to formalism, but in the context of physical phenomena, I don't know. It smells of reductionism, which is incoherent [0].
> To untutored common sense, the natural world is filled with irreducibly different kinds of objects and qualities: people; dogs and cats; trees and flowers; rocks, dirt, and water; colors, odors, sounds; heat and cold; meanings and purposes.
It's too early to declare that there are irreducible things in the universe. All of those things mentioned are created in the brain and we don't know how the brain works, or consciousness. We can't declare victory on a topic we don't fully understand. It's also a dubious notion to say things are irreducible when it's quite clear all of those things come from a single place (the brain), of which we don't have a clear understanding.
We know some things like the brain and the nervous system operate at a certain macro level in the universe, and so all it observes are ensembles of macro states, it doesn't observe the universe at the micro level, it's then quite natural that all the knowledge and theories it develops are on this macro scopic / ensemble level imo. The mystery of this is still unsolved.
Also regarding the physics itself, we know that due to the laws of physics, the universe tends to cluster physical matter together into bigger objects, like planets, birds, whatever. But those objects could be described as repeating patterns in the physical matter, and that this repeating nature causes them to behave as if they do have a purpose. The purpose is in the repetition. This is totally inline with reductionism.
> I don't know what a "simple idea" is here
To be blunt: it's whatever was in your head when you decided to handwave-away science in your upthread comment in favor of whatever nonsense you wanted to say about "Cartesian dualism".
No, that doesn't work. If you want to discount what science has to say you need to meet it on its own turf and treat with the specifics. Color is a theory, and it's real, and fairly complicated, and Descartes frankly brought nothing to the table.