A simple way to create holiday backgrounds is to find some coloring pages i.e. Buck Babies Holiday Coloring Pages and then go to Gif Works.
At Gif Works click the effects and select invert to reverse the colors to a black background. You can also make the white transparent using the edit button.
Resize to width 540 and you have a unique background.
Using grad colors in your body code and you'll have a very pleasent look.