I think of it as the 72's version of the billboard stripe....very bold statement that not many opted for
I'm not sure if the color keyed grille made it into 73 production but this videpo of a 1973 test car shows it http://www.youtube.com/watch?v=OwfFH70V5fE I also have another brochure page somewhere that shows a red 73 with a blody color grille