Be prepared for a million responses!!! This has been discussed/argued often. Many say "sun fade", but that doesn't explain why the fade is consistent, even in the shaded parts of the exterior. I personally believe it's a combo of chemical makeup of pigment, kettle heat, & exposure to elements over long period of time. Might be why interiors stand up over time compared to exteriors. People do tend to take better care of color kettles, so they are covered/sheltered more often than not.
Sent from my iPhone using Tapatalk