Question

Why are there only six fundamental colors: red, orange, yellow, green, blue, and violet?​

Answer 1

There are an infinite number of fundamental colors, if by "fundamental" you mean "spectral".

Answer 2

Answer:

Spectral colors such as red or green are composed of light waves of a single frequency. ... A prism splits white light into the fundamental spectral colors. Because the spectrum varies smoothly, there are an infinite number of fundamental colors.