[jacobolus]

Yeah, but "saturation" as you're using it is arbitrary, based on HSL or HSV, which are extremely simple transformations of RGB space, which means that it's based on the (arbitrary) choice of R, G, and B primaries for your screen. HSL/HSV were developed because computer hardware of the 1970s couldn't do large lookup tables or complex math with any kind of reasonable performance. There is really no excuse for them to persist to 2009, and that they are still being baked into specs is something of a travesty. They're essentially pre-20th century color theory pseudo-science, resurrected because anything better was too computationally expensive 35 years ago.

What you're looking for (to be perceptually meaningful, based on real psychometric data) is something like the "chroma" of the Munsell Color System. See http://en.wikipedia.org/wiki/Munsell_color_system