I just pulled the service parts ID label from the 2+2 that I have. The label shows L8535 U8535, which to me says that the car was originally all one colour. I've read from articles, and heard from other owners that the 2+2 was originally a partial build car from GM, which means that the cars weren't finished at the original production facility. They were shipped to a subcontractor for the installation of the rear glass and trunklid, nosepiece and striping. I'm wondering if the lower gray colour was also applied by the subcontractor during the final assembly. Sorry I couldn't provide more help.