A couple of possibilities (or improbabilities)

It sat on a turntable in the sunny window and got baked to olive green on all sides. (The illegible serial number is a hint that the piece has been 'fried in the window'.

It may have been treated to some chemical. Perhaps the store was sprayed for bugs and this piece got hit?

This may be the VERY VERY rare, "GI Joe Currituck". Only one prototype was made before HL decided they didn't want to be associated with war toys.

Two best choices:

1. Ask the dealer to replace it
2. Call HL 800-365-1219 and ask for customer service