Answer: Did you spot this quite quickly ? – the
robes on the King and the Page Boy on the left stamp
have had the colour blue "omitted", which
is a very sought after rarity in the stamp collecting
Once again, the Post Office and the printers of stamps
will do all they can to prevent this type of printing
error ever seeing the "light of day" ...
But as you can see, and happily for collectors, they
do not always succeed!