Most you might have come across websites, blackle.com and greygle.com which are two websites with Google Custom Search engine code included with it. But the way they advertised their websites gave them a good business opportunity.
What blackle.com did was, they made the background of the blackle search page as BLACK and claimed that if you use blackle instead of Google you can reduce the energy consumption with same search result. Similarly greygle.com also made the background as grey and advertised the same story. Fortunately they could convince many internet users to use their website instead of Google. But in fact, those website doesn’t reduce the power consumption, but may increase the power consumption compared to Google search pages.
See the Google Official Blog on this subject
Actual Comparison on blackle power saving claims