For those worried with energy consumption and all its downsides, when your screen is white, being it an empty word page, or the Google page, your computer consumes 74 watts, and when it’s black it consumes only 59 watts. Mark Ontkush wrote an article on his blog about the energy savings 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.
In response to this article Google created a black version of its search engine, called Blackle, with the exact same functions as the white version, but with lower energy consumption.
I personally prefer it, so blackle it is for me. Nice to know my new website is more energy efficient!!!