Ford listed multiple species of hardwoods in their part drawings for affected wood parts. They used what ever hard woods they had on the Iron Mountain property in the upper peninsula of Michigan
These sides are built of 3/4 inch hard wood closely fitted and bolted to steel stakes fitting securely in the Platform Body sockets. Both sides and ends are in one piece. The sides are bolted to the floor with two steel brackets on each side. The ends are held with tie rods running from one side to the other, the rods passing under clips on each end to insure holding them in place. The rear end is equipped with a specially built dump door, which breaks in the middle, being held in place by a strong clasp when closed. Measurements are as follows: Height 20 inches, Width 5 feet 8 inches, Length 6 feet 1-1/2 inches. Color: Commercial Green
More on that page about various other parts of the platform bed. Neil identifies the specified color mis-match with the common "Rock Moss Green." One imagines RMG would be the color of choice if the cab was RMG.