The colors used on your display screen can be an energy waster by the brightness of the color used. For example, Google is a prime example of a absolute white screen, that takes more energy to produce than, say, black. While I know not all of us can have the advantage of choosing a black over a white backdrop, its something to think about when putting a picture on your desktop, or keeping some windows down on the scroll bar, rather than keeping them up on your screen if you aren't using them.
Treehugger.com also wrote an article regarding this phenomenon:
"Take a look at Google, for instance, who gets about 200 million queries a day. Let's assume each query is displayed for about 10 seconds; that means Google is running for about 550,000 hours every day on some desktop. Assuming that users run Google in full screen mode, the shift to a black background will save a total of 15 (74-59) watts. Now take into account that about 25 percent of the monitors in the world are CRTs, and at 10 cents a kilowatt-hour, that's about $75,000/year, a goodly amount of energy and dollars for changing a few color codes."
Also, many people have created "black" versions of Google's popular search engine: