About 2 yrs ago I saw a similar error on a 1937 $1 note, where the front was blue and the back was green. This note sold on ebay for (if my memory is right) about $30. I do remember bidding up to $22 for the note myself.
I think that this is one note that you will have take caution with “Caveat emptor”, even if you have collectors or dealers look at the note for their stamp of approval, you just can’t be 100% sure.
Even the auction house that deals with thousands of note leaves this note in a grey area with the “probably due to” statement
I must say that the note is very interesting due to the fact it is defiantly a conversation piece among collectors, as we just don’t know the true store behind the missing colour.