A black background does not save energy
Google said it may actually increase energy used
"In the case of modern monitors (LCD's with either flash tubes or LED backlighting), the idea of black backgounds using less power is patently FALSE. The backlighting has to stay on, otherwise you would have no display at all - nothing to show the light colored text etc etc.
The reason that an LCD displaying white uses a TINY bit more power is that LCD panels need power applied to pixels for them to be 'open' or in an on state and let the light through. When no power is applied, they turn black/opaque/off and do not let light through. but we are talking a 2% saving here."
Tis' a joke.
Daed, how do I make an image my background?
body {
background-image: url("url goes here hnngggggg"); This is the url of the image, derp.
background-position: 100% 100%; This is the position on the page, relative to 100% of course.
background-repeat: no-repeat; You can have it repeat, like setting your desktop background to Tiled.
}