$4,248,000 The Treskilling Yellow, also known as the “three schilling banco error of color,” is a legendary Swedish postage stamp. Issued in 1855, it was supposed to be printed in blue-green for the three-skilling denomination. However, due to an intriguing printing mishap, only one example exists, and it turned out bright yellow instead. This unique stamp was canceled at Nya Kopparberget (now Kopparberg) in 1857. Over the years, it has changed hands among collectors and enthusiasts, fetching record-breaking prices at auctions. Notably, the most recent sale in 2010 reached a staggering $2.3 million. (Getty Images)