The 
HLS color space, also called 
HSL, stands for "
Hue, 
Saturation, Lightness." While the 
HSV (Hue Saturation Value) can be viewed graphically as a color 
cone or hexcone, HSL is drawn as a double cone or double hexcone.  Both systems are deformed versions of the 
RGB colour 
cube.  The two apexes of the HLS double hexcone correspond to black and white.  The angular parameter corresponds to hue, distance from the axis corresponds to saturation, and distance along the black-white axis corresponds to lightness.
External Link
- An explanation of HSL and how it differs from RGB can be found in the W3C's CSS3 Color Module (http://www.w3.org/TR/css3-color/#hsl-color).
All Wikipedia text 
is available under the 
terms of the GNU Free Documentation License