LeoKula said:
I think they might have made a few surf green.
They didn't make any officially.
They might have used some left over paint or odd mixes at the factory so it doesn't go to waste.
Fender did similar things with hardware (when stamps change going from one year to another), necks (when serial numbers change) or decals (when design changes) many times in their history.
Most likely your guitar has seen a lots of sunshine, or maybe lots of cigarette smoke that made it change it's colour more.
Or maybe one of the previuos owners simply refinished the body in different collor.
Here's a significant over time colour change on a real 1966 mustang:
