- Hue: The basic color in the color wheel, ranging from 0 to 360 degrees where both 0 and 360 degrees are red.
- Saturation: How pure (vs. dull) the color is, ranging from 0 to 100, where 100 is fully saturated and 0 is gray.
- Value: How bright the color is, ranging from 0 to 100, where 100 is as bright as possible and 0 is as dark as possible (black).
An example where color's value reduced by 20 (100, 80, 60):
See also this article in msdn to get more details.