Now, I’ve no idea how true this is, it would be good to hear your comments.
When your screen is white, be it an empty word page, or the Google homepage, your computer consumes 74 watts, and when its black it consumes only 59 watts. Mark Ontkush wrote an article about the energy saving that would be achieved if Google had a black screen, taking in account the huge number of page views, according to his calculations, 750 mega watts/hour per year would be saved.
As I said, I’m not so sure about this, are the savings too minimal? The fact the site is a custom search that has the potential to earn the owner money makes me wary, although of course you can be green and make money! Any thoughts?