Earth Hour will be today at 8:30pm local time. Non-essential lights and electrical appliances will be turned off for one hour. I’m not sure it is very useful, but at least it turns attention to climate change.
Some websites change their design from colorful to black (like Blackle). Some of the advertise themselves as energy savers. Well, I’m not sure about it. It used to be useful in the age of cathode ray tube (CRT) displays. Black color used much less energy compared to white color. Unfortunately liquid crystal displays (LCD) employ a totally different technology: they covers light to display dark colors. It means it doesn't matter the color you are displaying, the energy cost will be almost the same (or even more).
So use black background if you are using CRT displays – and use whatever color you favor if you are using LCD display.
And take part in Earth Hour if you wish. Probably I will. Turn off what you can for an hour at 8:30pm local time.