Farbtastic uses layered transparent PNGs to render a saturation/luminance gradient inside of a hue circle. No Flash, no pixel sized divs.
http://acko.net/dev/farbtastic
What makes Farbtastic better than others?
-It's true WYSIWYG: the color you click is the color you get (with the exception of +1/-1 rounding differences). Many pickers throw up an arbitrary gradient that's only a poor match.
-It uses the intuitive HSL color space rather than the more common HSB, which means it's easy to make a color brighter without touching its saturation, or vice versa.
-It's built on the compact jQuery library (http://jquery.com/)* and totals in at only 23KB, including images and CSS.
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*PS: check out the Javascript forum at Nabble.com (http://www.nabble.com/Javascript-f15545.html) gto see just how many JS libraries there are out there now... :o
Nice