Guessing at a category for this post!
I recently came across a copy of "POD Poster 103" from January 1963 for "Domestic postage rates, fees, and information" effective January 7, 1963, which marks the advent of the 5 cent letter rate in the U.S.
It is printed in blue, red and yellow. But on this copy, the red is inverted! Upright:
The same image, just rotated 180 degrees:
Lower left corner showing the POD imprint:
(I defined "upright" with the most colors correct and the fewest in error, which also coincided with the POD imprint being upright.)
Dimensions: 17"x22", folded into quarters.
No doubt rarer than the Dag Hammarskjold invert of a few months earlier!