Miss the GTK+ Color Selector on the web? JQGTK+ Color Selector is a JS port of it.

JQGTK+ Color Selector is an HTML5 jQuery plugin for color selection, based on the GTK+ Color Selector. It also helps with WCAG 2.0 color contrast compliance.

You can get the code and read the docs at Google Code: Project Hosting: JQGTK+ Color Selector and try a demo at Sequlr.com: Color.

Bugs, patches (especially for speedier use with older JS engines), suggestions, and concerns welcome.