I'm working on this atm. For now you can change the light/dark background colors:

(The OS is Ubuntu 11.04)
I made the colorpicker from scratch.

This development version don't work in latest Chrome stable (13), but it works in Chrome dev (14). I can't release the new version until they fixed it. The current version of WebJCS should run just fine in Chrome 13. If you have access to Chrome/Chromium 12, that works too with both WebJCS versions.
Here is a comparison between Chrome 13 and Chromium 12.

If you want to try out the latest dev version (with this colorpicker and some other new features) click this link.
You always find the current stable version of WebJCS on the Chrome Web Store.