A Real Oddball- #1319, 1966 5c Great River Road

I was sorting and cataloging stamps from an accumulation my dad left (he tore stamps off of the corners of every envelope that came in the mail for the last 80 years, it seems!).
I'm pretty new to this, but this one really stood out- weird enough that I set it aside, until I found another copy showing what it was supposed to look like. No idea if it's a printing error, or some sort of natural bleaching due to the passage of time, but if so, it was the only stamp in the whole box that's been affected. It's not from exposure to sunlight, that much is sure. Has anyone seen this before? I looked for similar ones online, but I couldn't find anything like it for this issue. I'm tempted to dump a cup of bleach on the other one just to see if it could have gotten chemically rinsed somehow, but I'm reluctant to destroy a perfectly good copy. Thoughts and feedback very much appreciated!

Very typical of sun fading. The reds, oranges, yellows fade out first.

Sun fading or chemical bleaching was my initial thought too, but these have been in a box in my mother's basement for as long as I can remember, and the other copy was normal, so it somehow seemed improbable. I guess it could have gotten bleached sometime between 1966 and early 80s, before they moved. Good to know about certain colors fading first. Thanks for the help!

There are far more stamps which are light-faded than chemically damaged. It takes only a few months - sitting on a desk, framed on a wall, etc.

There have been several threads on similar faded stamps. As an experiment, take a damaged stamp, cut it in half and write the date on the back. Then place half in a sunny window and the other half away from light. Come back in a few months or a year and see the difference.

One thread was on the yellow fading away from the Lady's slipper. Here is an example I cut in half on 8/28/16 and put half in the window and the damage from 11 months of bright light:




And a second example. Top strip in the sun since Oct 22, 2015. Middle strip since August 25, 2016, and bottom strip in the dark.

Wow, great information. I'm amazed it can happen so quickly. Thanks for posting the photos and for the education!