I originally became fascinated with color when I read the introductory chapter to computer vision in Robotics, Vision, and Control. It's really interesting how computer screens and cameras are designed to model out eyes and the colors we see are actually an illusion of sorts. All we see is combinations of red-green-blue which we can perceive as all the colors of the rainbow.
The name for this phenomenon, when two different combinations of light are perceived as the same color, is called a metamerism.
Anyways, it turns out the cameras cannot capture and screens cannot emit the full saturation of the color spectrum that we humans can perceive.
It all started with Wright and Guild's experiments that defined the CIE RGB colorspace.
CIE RGB colorspace.
This experiment had subject use knobs that three primary colors to match the monochromatic colors of the spectrum. Notice the that red goes into the negative! That means those colors around 520nm could not be reproduced using the three primary colors and some amount of red had to be added to the original monochromatic color in order for the subjects to match the two colors.
If you take these experimental results and plot them in 2D you get something that looks like this.
To get the CIE 1931 colorspace all we do is normalize this shape so that we get 3 positive numbers between 0-1.
And there you have it, the color gamut!