Well, if the many scrutineers at International Security Printers can miss it then so can I! The 81p in the British Inventiveness prestige booklet is sea green but it should have been holly green - the colour of the De La Rue self adhesive issued in March 2014. The sea green version dates back to 2008! So that is what all the fuss was about.
I am not sure it need make the stamp any more valuable, though, as it would have been a different item anyway, both as a new printer and with its security code.