I received this prepaid cover from UN New York. Cover is overprinted with additional value of 6 cents and there's also beautiful matching hologram stamp. So, everything is dedicated on this cover to the Headquarters of the United Nations in New York, a complex designed by a board of architects led by Wallace Harrison, and built by the architectural firm Harrison & Abramovitz. The complex has served as the official headquarters of the United Nations since its completion in 1952. It is located in the Turtle Bay neighborhood of Manhattan, on 6.9 to 7.3 ha of grounds overlooking the East River.
It's hard to show beauty of this stamp on scan, so i made this GIF file to show you changing of colors under different angles of light source.
Thank you, Mike!