GM Dealers at least the ones up until 2005 had a black chassis as FF said ARC was grey. Now the production runs were "lower" mainly split off the total overall sometimes. I have a few with an ARC run of like 12,000 a MAC of 3,000 and a dealers of 700...then they'll say total run of 15,700. Doesn't make them much more special since the chassis is different and the sticker says GM. I only prefer those because of the black chassis it looks better then grey to me. If you want GM diecast go for the exclusives like the 2005 Harvick GM/RCR Ann. colorchromes. There were 5 cars in that production all very low numbers. Any more questions just ask.