Are you using Blackle already?

Blackle saves energy because the screen is predominantly black. “Image displayed is primarily a function of the user’s color settings and desktop graphics, as well as the color and size of open application windows; a given monitor requires more power to display a white (or light) screen than a black (or dark) screen.” Roberson et al, 2002

In January 2007 a blog post titled Black Google Would Save 750 Megawatt-hours a Year proposed the theory that a black version of the Google search engine would save a fair bit of energy due to the popularity of the search engine. Since then there has been skepticism about the significance of the energy savings that can be achieved and the cost in terms of readability of black web pages.

blackle.com

Blackle claimed that their site saves electricity for having a black pages site, and as of March 2007 they have conserve at least 5,500 watt-hours.  And still issues went on about having black pages. And its true that black pages conserve electricity, but the fact that it is black, readability matters, since it lists webs from searching and it populates the page and readability becomes an issue. But if you really wanna conserve energy blackle could help, but theres no big difference between Google and Blackle when it comes to searching.

But if your using LCD monitors, color doesnt really give that effect on electricity, but on CRT monitors black pages saves at least 5% to 20% of electricity on a quick test made by Energy Star, they emphasized that it was just a quick test not a rigorous study.

So try Blackle now!!