I didn't at first understand why in addition to providing a background image it was also important to give a basic background color. I experimented with this setting up a few different kind of background pages and found generally that my image blocked any other color. However one image I did was to create a grey shape with noise superimposed. What was really nice about this was that any color I used as a background shone through the image so that the shapes remained but the color could be changed.