The SS396 used a signature blacked out rear tail panel on both Camaros and Chevelles starting in 1967. This was to denote a Super Sport 396 model. However, there are variations when it comes to Camaro PCs.
For years, there were stories that some of the late 1966 Chevelles carried the blacked out rear panel but I have never seen an original 66 SS396 with blacked out rear tail panel. To my knowledge, they were body color in 1966.