Google, who gets about 200 million queries a day, allways displays a white background with their famous colored logo. As an all white web page uses about 74 watts to display, switching to a black Google could save quite some energy, as someone calculated, up to 3000 MegaWatts per year.


However, though this might be true for CRT screens, for LCD screens the situation seems different : LCD crystals need an electrical field to turn them black (or rather, block the backlight).
OTOH, here's another idea. Turn off the computer. Or is that blasphemy ?