SG 456a 2½d Prussian blue. S superb unmounted mint example of this rare and famous error of colour. The item "SG 456a 2½d Prussian blue.S superb unmounted mint example of this rare and famo" is in sale since Tuesday, June 11, 2019. This item is in the category "Stamps\Great Britain\George V". The seller is "steveallen777" and is located in Hampshire. This item can be shipped worldwide.