About 20 years ago I searched for that question. After it's first 30+ years, one early 70's body shop repair when it was tapped in the rear, etc., that part was looking bad on mine. I found no documented answer or original photos but I did examine a local "perfect" one-owner, professionally restored, multiple POCI gold award winner Verdoro '68 RA1 (Also featured in the Sept. 2010 Pontiac Enthusiast). It showed the natural metal for that part. I then cleaned up that part on my Solar Red '68 to match.