Colour Mod is a colour selector tool that can be used on a website to let users dynamically change stylesheet colour settings. One of it’s most practical applications that I’ve seen so far is on Color Combos, where you can change any colour within a combo dynamically without any page refreshes.
The tool can be downloaded and plugged into your own website ( which also gives people like me a chance to study just how on earth it was done ) as well as a dashboard widget for OS X 10.4.
Even if you don’t end up using this tool, just take a look at how it is done. Clever and creative, I love it.