Just my opinion:
I have one hanging on the wall of my garage that looks just like yours.. I'm willing to bet that the original one is just faded out with years of washing/waxing/ ultraviolet exposure etc.... Wait until you put it on with the taillights and you will see that the panel flows much better with the darker color.
It is 50 years old after all!!
Seatbelts look factory original!! Great work!!