Thanks for all the info, I think a single colour box is very interesting - just not sure if it's $99.99 worth. I would have thought the proof sheets would be more valuable if left unfolded? Unfolded a full set of proofs (cyan, yellow, magenta, and black) could be framed for display around the resulting series 1 purple box.
This isn't a proof as such...As the others pointed out; it's just a partial-plate run-off kind of thing from the printer. Printed on regular box stock. So I'm pretty sure that there never was a sheet like this for each color plate.
There was a pretty big find of old printed unscored box sheets at defunct printers (some partial-plate, many full color), as the mythology goes, that turned up a lot of these. Either they were stored poorly by the person who first retrieved them, or they were stored poorly there. Some had bird droppings on them and other were chewed up by animals. But within them were some great vintage Topps pieces.
The problem with these uncut box sheets was their size - so many of them were folded and cut down for storage - though seeing one cut down and folded into box form is unusual from my experience.
I am fortunate to have quite a number of candy and gum display boxes from this same origin story. Here is one that only has the Cyan/Black plates, similar to this Wacky box:
Topps - Monster Gumsters Bubble Gum box flat - Universal Monsters - 1970s by
JasonLiebig, on Flickr