The premise is interesting. In summary:
It takes less power (especially on CRTs) to display a predominantly black screen. Google, which has a predominantly white interface, is estimated to be running 550,000 hours daily worldwide. Making Google black could save 8.3 Megawatt-hours per day worldwide!
Check out the full details in the full post and the interesting comments and links.
The point of note is: Small steps on a global scale must and do make a difference.
And this applies equally to technical changes as it does to attitudinal/cultural changes. Think the world is becoming more greedy and selfish? Give some of your time away and do some volunteer work. Think business is only for the bastards? Do something nice for your employees today.
(Thanks Mia for the heads up)