[68Conv400HO]

Coincidentally, a recent discussion on the 1st Generation Firebird website had a similar mystery with '68 Firebird. In that case the body had been already shot with the Verdoro Green as stamped on the trim tag and repainted blue within the factory before completing assembly.

See: Body Tag/VIN numbers don't match

Perhaps the orders got changed or commandeered for a different order early in the production process.

 

[68Conv400HO]

This one of mine was never white. I haven't a clue how it ended up Ash Gold.

It just shows that significant build order changes sometimes occurred after the Fischer plant started production. And, they did not go back and change the original stampings to reflect the new orders. In your case, the body had not been painted yet. In the Firebird example, it had.