Red Penny or Blue Penny
A Mauritian Blue Penny
Country of production	British Empire
Location of production	Mauritius
Date of production	20 September 1847
Nature of rarity	First stamps of the British Empire produced outside of UK and with wrong wording
Estimated existence	Unknown
Face value	Red: 1-Penny £sd Blue: 2-Penny £sd
Estimated value

The Mauritius Post Office postage stamps are amongst the rarest and most valuable stamps in the world. They are also known as the Blue Penny and the Red Penny.

Their value is due to two factors — they were the first stamps of the British Empire to be produced outside the United Kingdom and in their initial issue were printed with the wrong wording. They are therefore even rarer than they would have been had they been printed correctly.

Two stamps were issued, a red one penny (1d) and a blue two penny (2d). 1500 of each were issued from the first print run on 20 September 1847, many of which were used on invitations sent out by the Mauritian Governor's wife for a ball which she was holding that weekend.

The quirk of these stamps was that they had "Post Office" rather than the more conventional "Post Paid" printed on the side. Later print runs had "Post Paid" and any existing stamps from the original run can therefore easily be identified and authenticated. There is a traditional story which seeks to explain why the stamps were incorrectly worded, which has recently been challenged by philatelists.

The few surviving stamps are mainly in the hands of private collectors but they are on public display in the British Library in London, including the envelope of an original invitation to the Governor's ball complete with stamp. Another place where it can be seen is at the Blue Penny Museum in Mauritius.