In 1962, the Post Office made a 4c stamp with one of the colors inverted. When it was discovered, they reprinted 40 million of the corrected version so nobody would profit from the error.

As Wikipedia relates it:

The stamp, showing the yellow background inverted relative to the image and text, is also known as the Day's Folly after Postmaster General J. Edward Day who ordered the intentional reprinting of the yellow invert commenting, "The Post Office Department is not running a jackpot operation."