The Grey Background is a Watt-Reduction Theme.  Every milli-Watt counts.

  Some Snippets gleaned from the internet - Take the information with at pinch of salt, if you wish.  On the other hand, believe in the theme and contribute towards reducing consumption in every possible way.
An all white web page uses about 74 watts to display, while an all black page uses only 59 watts.”

Modern desktop PCs consume about 70W.  For CRT monitors add another 60W or approx 130 Watts.

Last year a blogger estimated that a black Google could save 750 Megawatt-hours of energy a year
You can save even more energy by just dimming the back light. 95% of the energy usage is lighting up the CCFL tubes inside the panel. Just turn them down a bit. It also may extend the life of the back light inverter, the tubes, and your eyes
The best screen saver is simply turning off the monitor! Computers and other office and laboratory equipment can be shut off nights and weekends when not in use. The energy to run a 300-watt computer/monitor/printer system operating 24/7 costs about $200 annually, but the cost falls to $50 when run 40 hrs/wk. UM recommends buying Energy Star equipment, which uses about 30% less energy when running and an additional 50% less energy in “sleep” mode
For CRTs - The screen is coated with a pattern of dots that glow when struck by the electron stream. Each cluster of three dots, one of each color, is one pixel. Certain colors, such as white, require all three dots to be charged, and are energy intensive to display. Other colors, such as black, requires no additional energy to produce and consume the least out of all the colors
LCD display technology is different from CRT technology, and the possibility exists that colors that are energy efficient to display on a CRT monitor (e.g. black) may not be as energy efficient to display on an LCD monitor. The Roberson study found that LCD monitors saved up to 3W by switching from a white to a black screen, and in no case did any of the LCD monitors use more energy displaying black than white.
Plasma displays are not popular for computer monitors. However, since they operate similarly to CRT technology, the energy differentials are similar.
For OLEDs - No comprehensive studies have been conducted of a comparison a white vs. black screens, but due to the nature of their construction, it is probable that displaying white consumes more energy than black on a OLED device.
Approaches -  Modify a color scheme of incoming web traffic at a high level, such as the corporate or country level. An entity with a large number of CRT monitors might convert the color codes, thereby producing a uniform color scheme for the entity as a whole. Countries such as India, China or Brazil, who have a large number of CRT monitors could save energy
Despite the criticisms and the arguments against using black or darker backgrounds, it still is a great idea of trying to help the environment every little way we can