Joel Henderson (see Letters to the Editors in 50(2), p. 4) stimulated me to investigate my stock of Sc#479 or KPC #C255. Joel’s question on Scott #479 moved me to look over my stock of this stamp. I was in Korea when that stamp was issued and for years afterwards, and I did not run into that color of grey-blue. Also, I wonder on the basis of how many stamps you claim the color change. A full sheet of stamps or a real good block of the stamps would be pretty good evidence of a color change.
My personal feeling is that you have a sun-blasted stamp regardless of gum or lack of gum. I have in the past sun-blasted some Kore-an stamps to see what happens, and if your supply of the stamp is adequate, you might sun-blast one of your #479 to see if it changes to grey-blue. Put the stamp in clear plastic, tape it to the window, and let the sun blast it for two or three months and see what color change has occurred. Keep observing the stamp as the days go by.
(Image from KoreaPost. Cover image from 사랑화폐&우표)
(Originally from KP August 2005, Vol. 50, No. 3)