here here :

to this
The seven colors are classical physics-optics. RGB and CMY are adopted in order to simplify the creation of devices (monitors, printing machines). In the latest CMYK

Classical physics-optics is that the iris spectrum is uninterrupted. Colors are used only for convenience. someone on seven, someone on six (in some English-speaking countries), someone on eight (to six main, where blue-blue one color, add ultraviolet and infrared), someone in general on 256 :):):)
Teach the match.

= is

The gods! It is done! Is there anyone who understands it? All blessings to you, my friend!