[The text from this post came from an email chain letter, of all things, but it checks out.]
If Google had a black screen, taking in account the huge number of page views, according to calculations, 750 megawatts/hour per year would be saved.

To test out this theory, Mark Ontkush from ecoIron created a black version of Google's search engine, called Blackle, with the exact same functions as the white version but with lower energy consumption for its users.

Help spread the word… use www.blackle.com.

[ The original theory ]