Orange man!! Everything is silver these days. it gets boring! classy but boring!
Only exception is if you have a macbook air. The silver nano, with its black clickwheel, would exactly match the silvery MB air with its black keypad
No matter which one you get though, if you tire of the color you can probably get a skinny case somewhere and cover it up. So in that case, probably best to get the bright orange one again, since like others have said, a silver case is easier to come across.
I think I'll be getting the green one