The seat has been re-inserted with non original fabric. The Blue "crush vinyl" could be the original.

The '65 F100 Standard Cab I bought new had blue crush vinyl, but AFAIK, it was a different shade of blue than 1966.

 

It was funny, but today as my son (14 yrs old) and I were taking the seat out, my wife screamed because she saw a bull snake climb up the channel where the door hinges are and into the dash area. It was hard to get either one to help until I extracated the snake.

 

lol, that'll do it