Themes can be written using Liquid, a Ruby library and Rails plugin focused on delivering simple and secure templating. Creating a new theme is easy, installing an existing theme is even easier.
Chameleon 0.6.0 includes a simple default theme showcasing the features of Chameleon, and a port of the famous Simpla and Scribbish themes.

You can download Chameleon 0.6.0 (Beta) at http://chameleon.wikidot.com/download, and follow the instructions in the README included in the package to install it. These instructions and a lot more information are also available on the website, at http://chameleon.wikidot.com.
Since Chameleon is still in beta, some problems might occur. Report any issues in the bug tracker at https://bugs.launchpad.net/chameleon/.