Its possible. Depends how skilled and helpful the person is who you deal with. I had a 205 gti a few years ago which had been red but faded to almost orange. The bloke in the shop brought all his colour cards out to the car and spent about half an hour comparing them until he found one which looked right (some Nissan colour iirc) when I sprayed the wing on the car with the aerosol he had mixed up it matched beautifully. 
It wasnt a metallic colour though, and I believe silver is notoriously hard to match.
I worked as a colour matcher in the printing industry for a *long* time.
silver is VERY difficult to match, but it is also very exposure-resistant.
If you get a matching tin, it should match even older paint,
the worst colours for fading are reds navy (reflex) blues, and some pinks/purples.
they are also the easiest to match

(at a particular point in time; unless the same pigments are used, newly applied colours can change more than the colours they are supposed to match - so they might match now, and look a thingy in 12 months time).
course, you could do like the previous owner of my last van did -
painted the entire thing with white dulux gloss with a brush