HSV

Hue, saturation, value -- color split into which hue, how vivid, and how bright the brightest channel reads.

HSV derives hue $H$ (shared with HSL) from the normalized RGB extremes $C_{max},C_{min}$ , then sets $V=C_{max}$ (the brightest of the three channels) and $S=0$ if $C_{max}=0$ else $\Delta/C_{max}$ where $\Delta=C_{max}-C_{min}$ . A pure, fully-saturated primary always has $V=100\%$ , since that primary channel is itself running at full scale.