These stamps were issued by Colombia on 22nd August, 1950 on the occasion of the 75th Anniversary of the UPU.
The stamps depict different orchids and the 18c stamp shows the Santo Domingo Post Office.
580 - Masdevallia Chimaera
581 - Odontoglossum Crispum
582 - Cattleya Labiata Trianae
583 - Masdevallia Nycterina
584 - Cattleya Dowiana Aurea
585 - Miltonia Vexillaria
586 - Santo Domingo Post Office