Basics of colorimetry
Colorimetry

The visual appearance of color is three-dimensional in nature. It involves three psychosensory parameters corresponding to the subjective sensations of hue, saturation and luminosity. Hue is defined by the words blue, green, red and so on. Saturation expresses the degree of coloration, as opposed to the quantity of white radiation appreciated in colored radiation; a color is less saturated the more it appears washed white. Finally, luminosity, an achromatic factor, refers to the level of colored stimulus; it varies from a maximum non-glare value to the absence of light (black). It's easy to see how, by varying these three parameters independently of each other, you can achieve every imaginable color sensation.

But while trivariance...