Pop Hovers

A website (http://www.popagency.com/) has text boxes that have a white background with text.  As you hover over the box, the background changes to black and the text changes colors.  As you leave the box, the colors and text return to their previous state.  You can vary these effects.  Another well done web page worth checking out that uses this technique is ABAP HELP (http://zevolving.com/).