google black

Nicola Davies posted this good energy saving idea by google. But why don't google just turn their pages black, or even better grey as this is better for non burn out on the eyes when viewing screens.
http://www.blackle.com/
Mark Ontkush wrote an article about the energy saving that would be achieved if Google had a black screen:
When your screen is white, be it an empty word page, or the Google page, your computer consumes 74 watts of energy, and when it's black it consumes only 59 watts.
Taking in account Google's huge number of page views, according to his calculations, 750 mega watts/hour per year would be saved.
In a response to this 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.