Hello there! I jumped into your account to take a look, and I think you may have resolved this by selecting a different template, one that has a white background, in the campaign called "Untitled Mailing."
I'm thinking "TrusteeWeekly10/04" is the campaign you were referring to before, and there, you can change the background color by clicking Backdrop and changing to white:
Let me know if you're still having trouble! I'm going to tweak this topic's title a bit because I bet others have this same question. :)