I used to do pinstriping and decals, especially for repair shops who needed to replace or match factory work, so I've done a lot of matching factory colors. I'm familiar with the Oracal, 3M and Avery colors from that website, although I'm not very familiar with Arlon. I'm also not familiar with Rubicon decals specifically but I'm familiar with Jeep decals in general and my 01 sport is listed as dark silver metallic so I assume it's the same decal.
I'm saying all that to say this..
I don't have a freaking clue.
Ok, I do have a clue, but not a great answer. The factory color is really a dark grey and if they have any metallic in them, it's hard to see. I'm not aware of anything to match the factory color, assuming yours is factory and is the same color as I'm familiar with. Oracal and Avery have nothing close. 3M makes a pinstripe close to that color, but they quit selling large rolls of vinyl in those colors years ago. There's only one company I know of that makes a color close to it and I've never bought that color from them to know for sure.
The Avery Dark Charcoal would be my choice for closest match. It will be a bit lighter and more metallic than factory. Black would be a bit darker obviously but would match the lack of metallic in the factory decal. Matte black would also look good but it's matte, no factory decals are matte. I'm speaking as if I'm holding these colors up beside a factory decal and trying to find the one perfect match. It would be hard to tell a difference with any of them once they're on the vehicle. No one will ever notice any difference.
