It's the stripe I described...a double pinstripe at the lower body line running from the front bumper to the rear. My first '68 had one but I don't have a pic of it where the stripe shows clearly. You don't see many cars with them.
About the only pic I could find is of this MODEL car. Of course, the stripe is a little 'off scale', that is, kinda thick compared to the actual car.
Coincidentally, this model is exactly like my first GTO. Mayfair Maize with black interior and black Rally Stripe.
This is the best pic I can find of my old one from '82. You can see the stripe at the lower front fender..
