Infotix -- A Technology notepad

Apparently, an all white computer screen, such as an empty Word page, or the Google page, uses 74 watts to display, whereas a black screen consumes only 59 watts. So claimed Mark Ontkush in a post on the ecoIron blog in January. Doing a few back of the envelope calculations based on numbers of users per day and wattage for different coloured screen from EnergyStar, Ontkush figured that the energy saving would be 750 Megawatt hours per year if Google had a black screen.
And so, with the help of Heap Media, Google created a black version of its search engine, called Blackle.

The Wall Street Journal did some of their own calculations, which challenge the energy-saving claims of Blackle. In a blog post from May, they point out that the "savings are most likely to accrue from older CRT (cathode-ray tube) monitors, rather than the more modern, energy-efficient LCD (liquid crystal display) screens that dominate the market (representing three quarters of all monitors world-wide as of last year, by some estimates)." They did some tests using Blackle, Google and the New York Times on a CTD and LCD monitor and found the difference "so slight as to be within the margin of error for the power meter".