Arnheim is kind enough to distinguish between "generative complements" and what he calls "fundamental complements", (though I would prefer they be called "perceptual"). He warns specifically against confusing perceptual color and color-in-the-world. By making that distinction, Arnheim validates BOTH systems, rather than attempting to invalidate three-primary systems (as this article appears to do).

The article calls RGB and RBY color "wrong" and unable to "stand up to even minor scrutiny".

Arnheim calls them "generative".

I claim their generative nature (that they inform how to create color) is why they are taught in schools. I'm not denying the four-color idea; I'm just saying it is based on a different definition of color, and different intended use of color.