Would changing Google to black really help save the environment? I'm not an expert to tell how accurate these figures are or whether it makes a difference at all (somebody please call the Mythbusters)! Still, it sounds like a good idea. At the very least, how we can conserve energy by doing little things is thought-provoking.
To change the background color of Google and Youtube, you need to download the Stylish add-on for Mozilla Firefox (don't tell me you are reading this blog with some other browser) and install your favorite userstyles to customize. That's it!