There are around 18 different versions of black google online. The best one Ive found is www.cleanblack.com.
Cleanblack is the only version that allows you to change the text
colors of the google search results. Try it yourself by going to www.cleanblack.com/theme/
The energy saving is true, but only in CRT monitors.you can try another similar web but with more functionalities:http://www.blackoogle.ushttp://www.blackoogle.co.ukFrench engine:http://www.noirgle.frbye;)
Of course you don't save any energy with this. It's a good marketing stunt....