User defined page colors

Im looking for suggestions on preexisting engines or plugins that could
handle this:

Basically I want to offer users on a site the ability to change some
fonts maybe layout switching of some sort.

Is there anything out there that can accomplish this right now?

If not id like to discuss scenarios on how to accomplish this; its
something others would want to use as well

An engine would seem to be the right choice

Ive been experimenting with this and it should be fairly simple to

In your action you define something like


And then in your layout place that with the


Of course being able to dynamically adjust css files would be
interesting as