Sweden

The Swedish Three-Skilling Yellow is one of the most valuable and sought-after stamps in the world. In 1855, Sweden issued a series of stamps in different denominations, each in a specific color. The three-skilling stamp should have been printed in blue-green, but a small number were mistakenly printed in yellow — the color designated for eight-skilling stamps. This extraordinary printing error went undetected for years until a schoolboy discovered it in 1886. Only one example is known to exist, making it one of the rarest stamps in the world. This cover displays the unique yellow stamp with a clear period cancellation, representing an artifact of incredible rarity and historical importance. The Three-Skilling Yellow has sold at auction for millions, placing it among the most valuable objects per unit of weight in existence. Its story combines human error, accidental discovery, and the pursuit of philatelic perfection.