The Red-Green-Blue (RGB) Colorspace

The Hue-Luminence-Saturation (HLS) Colorspace

When we think of colors in everyday life, we usually think in terms of "red", "green", "violet", etc., in other words, the Hue of the color.

In the HLS Colorspace, Color is not defined by Hue alone -- but rather HLS, Hue, Luminence and Saturation. Hue is just one component of a 3 component system to describe color. Defined by HLS, gray is independent of hue because its saturation is zero. The luminence is midrange between brilliant (white) and dark (black). If you were to take gray, increase the saturation midway and set the hue to red, you would have pink. Similarly Lime can be described as desaturated Green. So gray is a color that can be designated by HLS coordinates just like any other color.

The eye does not use HLS to determine color, so a better way to understand the color of light is by RGB components. RGB values can be converted to HLS by vector addition. The eye determines the level of R, G, and B by 3 different frequency sensors. When all three are present, at the proper levels, that is White when full brilliance, or Gray when midrange. When the ratio of Red is higher than a gray mix, that is pink. When only the Red is sensed, that is Red. So Lime is Green that has a little blue and red mixed in. The eye sees yellow as Red and Green with no Blue.