Mark Ontkush at ecoIron did some math starting with the Department of Energy data that showed CRT monitors consume less power displaying dark colors than light and determined that redesigning Google’s site in black would save 750 megawatt-hours per year (assuming that 25% of computer users still haven’t upgraded to LCDs and are using power-hungry CRTs).
The results were so dramatic he redesigned his own site and developed a low wattage palette that uses only about three or four watts more than a completely black screen (white is to be used only as a text or accent color).
What can you use it for? Any application that is displayed on a device that uses CRT, Plasma, or OLED technology. Any device where white costs money — handheld units, web sites, TV.