上禮拜調整螢幕選項，有興趣查了一下...
HSL stands for hue, saturation, and lightness.
HSV stands for hue, saturation, and value.
http://en.wikipedia.org/wiki/HSL_and_HSV#Saturation
http://en.wikipedia.org/wiki/HSL_and_HSV#Converting_to_RGB
Fig. 23. A graphical representation of RGB coordinates given values for HSV.
V(1-S)<= RGB values <= V