You could trim one of the cloud backgrounds to make it a squiggly line of clouds with just white space (or some plain color) in the middle. This is what they often do in tv shows, but with fog.
For now though you could just use clouds 1 or 2. I"m sure people would catch on to the convention. If they don't, add a narrative box.
You know a background I'd REALLY like to see is a gigantic tv screen that takes up the whole frame. Then you could cut away from the tv prop and watch what's on the tv. Maybe add a couple different background scenes on the tv, so when you add characters to the panel, they're in a game show, soap opera, porn, whatever. (You could do the same sorta thing with the pc prop.)
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what if nigger meant kite