1883, King Leopold II., De La Rue archive appendix sheet with 10 imperforate colour proofs (10 c. rose, 20 c. olive green, grey, cobalt-blue, emerald, aniline scarlet, orange and chocolate brown, 50 c. violet-blue and 1 fr. bright purple) and a cut-down sample label in pale brown; all annotated in manuscript for the new values in the UPU colour scheme, required in the Congress of 1878. A most attractive and unique item.
