This is one of these things that when you see you say "How didn't we think of that before?" In January this year a popular green blog ecoIron suggested to change Google site background to black and by that save about 750 Megawatt-hours a Year!! Here is why:
"As noted, an all white web page uses about 74 watts to display, while an all black page uses only 59 watts. I thought I would do a little math and see what could be saved by moving a high volume site to the black format."

Multiply that in 200 million queries a day and bingo, you’ve got $75,000 worth of energy saved. As Google didn't really react to the message, someone actually executed this smart (but not proven yet) idea and developed Blackle ( http://blackle.com/) -- a black version of Google!

I've been always into black, so the black Google couldn't feel more natural to me, although it does remind me the early days of the Internet. I love the idea that color can save us some resources, so I'm officially moving to Blackle!