Just talk to me if there's problems like these. I don't frequent this wiki anymore but I can always try to fix things.
This was caused by Wikia's changes to load an iframe (basically another page) as the editor. This causes the CSS definitions to treat that page as the main page and splat the background in there as well. It just took me 5 minutes to figure out what's going on and to set an override. You shouldn't see the background now.
Hit Ctrl+F5 to force your browser to reload the CSS if you're still seeing it. You only need to do this once.
I don't know why, but for some reason I edited the Milky Way Wishes page, and it didn't default to the visual editor like it usually does
Some pages can't be loaded in the VE as they have complicated code or markup, but I could load the page you mentioned, but I had to switch my preferences first since I use source mode exclusively. It might be something to do with your preferences or it might be a hiccup on Wikia's end. Either way, I'm afraid there's nothing I can do about it.