Could a white-on-black Google save power?

Kris_J writes: "Rising Phoenix Design's BlackBack theory says that since white costs more power to display than black on a CRT, web pages should be light text on a dark background. One idea then is that since Google is the most popular website on the planet, would there be a significant global power usage reduction if they changed their design to white text on a black background? At the very least, I reckon they should try it for three days and find out."