Great Britain SG 628, 628b 1961 Queen Elizabeth II 10d. Turquoise colour omitted. Unmounted mint. With Cert.

Great Britain 1961 Queen Elizabeth II 'European Postal and Telecoms Conference'.  10d. turquoise, pale green and Prussian blue.  Error, 'Turquoise omitted'. Superb unmounted mint condition (with normal for comparison). British Philatelic Association Certificate No. 64,446 (2005). ONLY 18 EXAMPLES OF THIS ERROR EXIST MAKING THIS AN EXCEEDINGLY RARE AND IMPORTANT  STAMP FROM THE REIGN OF QUEEN ELIZABETH II.  AN EXHIBITION ITEM.