Rarity does not always equal desirability.

While I have nothing against silver, it's never been on my list as a "must have" color. I really can't see it adding any value to any car, be it an SRT or whatever. Since the Challengers aren't out just yet, to use the Charger SRT8 as an example, I see Inferno Red as a possible collector color, mostly because they only used it on 2006 - in 07 they replaced it with the inferior and much less desirable TorRed (IMHO), although they did keep Inferno Red as an option on the 300 SRT8.

A Plum Crazy SRT8 will definitely have some collector value, as I'm sure will the Detonator Yellow and Surf Blue Super Bees... but the regular colors, TorRed Silver and Black, I really can't see as having any infinite collector value at all.