Great Britain 1851 2d violet blue on thick Iavender tinted paper Plate 4, SG15aaThe rarest shade of the 2d Blue The 2d Violet Blue. Less than 20 known surviving mint examples Great Britain 1851 2d violet blue on thick Iavender tinted paper Plate 4, SG15aa. A superb unused, with original gum, good to large four margin example Ieltered 'RF' of this rare shade variety. Beautiful fresh colour and gum. In 1851 a few sheets of the new Twopenny Blue were printed and something went wrong The printing ink reacted with a bleaching agent in