Update: Looks like if I use an 'Images' design (vs. a 'Headlines' or 'List' design), I won't get this "gray replacing white background" issue (issue attached). I noticed that once I delete the default image from some of these 'Images' designs, the image placeholder box is white (attached), whereas this box was gray for the 'Headlines' or 'List' designs that was having this issue – I figure this might be an indication of where this issue might arise.
Hope this helps solve the issue or at least help others find a work-around.