Hue, brightness, and saturation are the basis for the description of a psychological sensation of color, but the last I knew none of these parameters were defined quantitatively. The primary colors are red, blue, and green and the subractive ones are yellow, cyan, and magenta, where the last two are obviously not pure spectrum colors, but the first four are not defined quantatively in terms of a range of spectrum colors from any given source of radiation.

We could undoubtably make the system work for primary colors and yellow by chosing spectrum colors for blue, green, red and yellow, but that doesn't mean that the choices we make are the only possible ones that would fit the loose definitions.

It's perhaps unfortunate that the term 'color' is used in both the psychological system and the physical one loosely describing a wavelength of visible light (spectrum color).