Verry interesting!!!
I do see in the brochure that they mention the 6 different colors and I see the painted grill on the Cuda. You don't see many cars with the painted grill and if you do it's easy to assume that they were painted by the owner at some point in thier 30+ years old life. Sounds like it's pretty rare and seems as though it's the whole grill. Initially I was thinking that it was just the inside lip of the grill opening (usually red) but after looking at the brochure it looks like the whole grill is painted.
I wonder what the 6 colors were? I wonder if there were a couple shades of grey/argent? Could've been just variations of the argent paint.
In the 1974 brochure they only mention an argent grill, no color options so it may be a '73 only option? I dunno...