That's tough to say. Chevrolet didn't keep any records of this. If I were to guess I would say some of the rarely seen exterior colors are Satin Silver, Bahama Green, Lagoon Aqua and Azure Aqua. The rarest interior colors would have to be silver and white. Silver was only available with 4 colors (Red, white, silver and burgundy) and white only 3 (Red, white and burgundy). From that info, Silver/Silver might be the rarest!!
Ross