Color theory is both the science and art of using color. It explains how humans perceive color; and the visual effects of how colors mix, match or contrast with each other.*
Color theory also involves the messages colors communicate; and the methods used to replicate color.*
*The fundamentals of understanding color theory_by Kris Decker 2017 99DESIGNS
Six color tones comprise a heptave scale, for example, as the next tone below visible red as so-called "infrared" is an invisible violet tone one "heptave" lower than visible violet, i.e. half the frequency, v/2, and twice the wavelength, 2λ, of visible violet.
Similarly, "ultraviolet," the next tone above visible violet, to humans, is an invisible red tone 2v and λ/2 of visible red, a heptave above visible red.
Additive Color Emission https://m.youtube.com/watch?v=KZ-mEddsYqo
So, from about 700-400 nm, we see but almost one whole heptave among vast multitudes of heptave ranges in the entire electromagnetic spectrum.
NOTES: We normally hear about 11 octaves from 20hz-20,000hz.
Our eyes are the only brain tissue exposed to the outside world and environment.