In September 1847 coloured squares of paper were stuck to envelopes and used to send out admission cards to a fancy-dress ball on the tropical island of Mauritius. No-one at the party would have guessed that the envelopes bearing these stamps would one day be worth more than a million dollars.
When a two pence 'Blue Mauritius' surfaced on the fledgling French stamp-collecting market in 1865 it g...