My wife put me on to this web site. Apparently web pages with white background take more energy to display than black colour backgrounds. So the logic goes that if Google, which is one of the most used websites, were to be redone in black, then we would be saving Megawatts in electricity. That call was answered by an Australian group Heap Media who've set up Blackle. Yes, here you can search Google in black.
The claims of power saving are more applicable to CRT (Cathode Ray Tube monitors, the TV-type boxes) monitors rather than the LCD (Liquid Crystal Display) monitors. In fact it's thought that showing black consumes more power than white on LCD monitors. So the debate can go on.
This reminded me of the first Webstock conference, held here in Wellington. At first the organising group had set up a very well designed site with lots of images, bright backgrounds and detailed fonts. Then apparently an email circulated that designing these kinds of sites causes more power to be consumed when viewing on the computer. Being the caring-and-sensitive types, the group promptly took down all the styling until the web site was normal text on plain-gray background. This would have satisfied the green-minded, but by the time the conference was about to commence, lo - the styled version was back without any explanation. Somebody must have figured it out - you can't hold a prestigious conference with a dull, boring online website.
See related article.