Proof Master colour trials (4), comprising perforated (3) in green, blue and grey marked with suggested values for ½d., 2½d. and 4d. respectively, and imperforate in grey-brown marked for 6d., affixed on piece (144x200mm.) with the ½d. and 2½d. trials bracketed and marked "Colours settled by the International Postal Convention". A colourful and unique group. Photo