"An all white web page uses about 74 watts to display, while an all black page uses only 59 watts."

This years Earth Hour, 8pm on March 29, 2008, google temporarily switched there page from a white backround with black text, to a black backround with white text.
There have been quite a few opinions about if this actually saves energy, and the eventual outcome seems to be that in most cases, there is indeed a slight decrease in energy used to display the color black...