The example given uses Google, but it applies to all web pages, and to be honest I was amazed!
An all white web page uses about 74 watts to display, while an all black page uses only 59 watts. See what happens when you do the math on Google's home page. Astounding.
So what does happen when you do the math? Click here for the full article.
Now what if all web pages were black or dark in colour ... just think how much energy that could save!