> HSL is the same idea, but more comprehensive. H encompasses pretty much all of R, G and B, and S and L allow for variations in... err... saturation and luminosity. :-}

Any color that can be represented in HSL (or HSV, where V is "value") can be represented in RGB and vice versa.

Saturation is a measure of how much "white" is in the color. Value is almost the same as "brightness," like on a TV screen.