TIP - To keep your main (html) - page neat and easy to read, you can put the head or body javascript into an external .js file (minus html tags) and reference it from your page thus -
<script language="JavaScript1.2" src="MY.js" type="text/javascript"></script>

This script is easy, compact and it will work in browsers with javascript disabled.

Background color-changer

Right-click - 'select all' (ctrl-a) then copy (ctrl-c) and paste to 'BODY' of your page.

You can customise size, position, scrollbars etc, of pop window (see script).