2.6 million dollars was paid in 2011 in Basel for a Sicilian Error of Color Stamp.
The rarest and mysterious stamp of Sicily is the error of color of 1/2 grana. 
The stamp is rare for several reasons. First of all, it has an error of color. 
It was supposed to be issued in orange color. Instead, in 1859 the stamp was issued in blue. 
Secondly, there are only two stamps known to exist today.
They were exhibited first at the Manchester Philatelic Exposition in 1899. Then stamps were separated sometime before the private treaty sale in Italy of a portion of the Ferrari collection.
The Sicilian Error of Color Crypto Stamp-1859 seems to have a secret message in the bearded man's speech