Two Penny Blue

The Two Penny Blue (or 2d Blue) was the world’s second official adhesive postage stamp. It was issued in the United Kingdom in May 1840. It was more or less the same as the Penny Black. 
It was intended that the 2d blue was to be issued at the same time as the Penny Black. However the earliest post mark seen on a Two Penny Blue was the 8 May 1840 which is two days after the penny black was issued. The Two Penny Blue is much rarer and more expensive than the Penny Black.