Yes, you cannot choose a plain white "background" from the options. However, the way the program works is whichever option you choose last is the one it uses.
So if you choose the background "color" as white and click on save, it will negate any background "picture" that is chosen. So whatever is listed for background picture won't matter. Hopefully that makes sense and clears it up?

So while you cannot opt out of having a background picture technically selected, it wont matter, as you won't actually be using it if you choose the white "color" option as the background and save it.