I was working on a project recently that required a color picker. It didn’t take long for me to find Colour Lovers’ free DHTML Color Picker. It’s easily the best color picker script out there (that I’m aware of).
The picker works well in most browsers, and it works much like the picker in Adobe Photoshop. It’s fairly hackable too, if you want to customize it a little. Theoretically, you could take-out the RGB, HSV, and CYMK forms if you put your mind to it, for example. The script makes it easy enough to integrate into most forms (though I had to play around for awhile to get it working just right for me).
This is a good script, and well worth looking at if you ever need a color picker.