Mark Ontkush did some calculations about how much power is consumed when a computer screen shows white backgrounds rather than black. He tells the story of how this played out:
In January 2007, Mark Ontkush, the owner of the ecoIron blog, suggested that a large amount of energy could be saved if Google switched their home page from white to black. The initial savings was estimated to be 3000 Megawatt-hours a year; this was later rounded down to 750 Megawatt-hours, after an error in the calculations was found….