South Africa Postage Due 1927 3d Perf'd Plate Proof / Trial Bloc

POSTAGE DUES: 1927-28 3d deep blue & blue PERFORATED PLATE PROOF / COLOUR TRIAL lower left corner block of four of complete design on UNWATERMARKED PAPER, Perf 14. VF/UM, couple light internal gum wrinkles, see scan. This colour combination was rejected in favour of the issued black & blue. Scarce proof for this issue. See additional image below.