[css question] Background replacement

Is it possible to use CSS (or something else) to be able to replace the background image of a page? I have found several image replacement technique, but my limited understanding of CSS suggests that this won’t work on a background.

I was thinking of several square shapes that you could click on which would change the background from one image to another (and perhaps change the overall color scheme of the page).

Right now my overall CSS file has the convention for making the background

body
{
background-image:url(Images/Background.gif); /Makes Background/
}

Could I have different ones for each color or something? When you click the box it would switch the CSS sheet?

Anyways, just wondering, thanks,
Overshee