I had a 79 Camaro with code 29. I'm pretty sure it was called Midnight Blue.
People called it black a lot too. A buddy always called it green, but I figured out pretty quick that he was color blind.
Have you ever thought that maybe he wanted a better ride, or to be able to haul motocross bikes or 4'x8' sheets with the tail gate shut?
Or possibly wanted a truck to actually be used for work.