It looks like the background image uploader loads empty images even when you don’t add anything. I’ve noticed this myself on a local install. The way I fixed it is to upload an image to each section, then remove it, and that clears it up.
The reason you’re seeing a white background is because of the blank image on top. So try and add/remove an image on each section and that should work. Hopefully I can figure out why it even does that in the first place.