On this day in 1840, the Twopenny Blue, the world's second adhesive postage stamp, was released by the British Post Office. Issued just two days after the Penny Black, this stamp is often overshadowed by other early stamps. To celebrate the 175th anniversary of the Penny Black, the Royal Mail did issue a souvenir sheet featuring both the Penny Black and Two Pence Blue. These stamps were often canceled using the Maltese cross, which was also used on the Penny Black and Penny Red. More information about canceles and engraving of early British line-engraved stamps can be found in this article. 

Examples of the Maltese Cross cancelation and Royal Mail souvenir sheet

21 years later, St. Vincent issued its first stamps in denominations of 1d and 6d. They were intaglio printed by Perkins, Bacon & Co. of London. The design featured a profile of Queen Victoria. The stamp had a perforation of 14-16 and no watermark ( although one is present in later variants of the stamp). 

An example of the first stamp of St. Vincent

In 1946, the French colony of Wallis and Futuna islands issued its first air mail stamp. The design features an angel flying above tanks, celebrating the victory and end of World War Two in Europe. Both perforate and imperforate varieties of the stamp exist. 

An example of the stamp 

In 1981, the first philatelic item to be sold for a million dollars was the cover bearing a copy of the Alexandria, Va. postmaster's provisional. The record price was paid at an auction held by David Feldman Ltd. in Geneva, Switzerland. It had sold for ten thousand dollars at the 1955 Caspery Sale. The cover is known as the Blue Alexandria or Blue Boy. More information about this famous cover can be found in the interview with David Feldman, part of our Famous Philatelist Interviews.  

An image of the cover