Blackle is a website powered by Heap Media, which aims to save energy by displaying a grayish-white background. Blackle claims having saved nearly 6 MWh of electrical energy up to December 2016, a claim currently under dispute. For comparison, the average American household consumed 11 MWh of electrical energy per year.
The concept behind Blackle is that computer monitors can be made to use energy by displaying much darker colors. CRT and LCD monitors. There is a dispute over whether there is any energy saving effect, especially for users of LCD screens, where there is a constant backlight. This concept was first brought to the attention of Heap Media by a blog post, which estimated that Google could save 750 megawatt hours by using it for CRT screens. The homepage of Blackle provides a summary of this issue.
Black Google Energy Saver Search Blog: BLAck goOGLE