I don't think the note is cleaned. Technical grade and appearance are not that closely related. I have seen plenty of well-circulated notes with hardly any soiling, like this note, and they were original. A note can get folded and crumpled without getting dirty. It's also quite possible for a note to get dirty and remain firm, and we see lots of those around. Lots of older notes are stained, probably from being in dirty pocketbooks for a long time. Anyhow, if this note was cleaned, the green tint on the front should have been affected as well, and this is not the case.
The torn corners on this shinplaster suggest it may have been mounted, and if that's the case, prolonged exposure to light may have caused the green colour to fade and alter. Of course, it's only logical to ask "Why would someone display the BACK of the note?" Maybe it was part of a two-note display, one showing the face and the other the back. Or maybe we're looking at chemical damage not related to cleaning. Maybe the note was in contact with some unstable material that leached into the back.
