restoring old stuff - matching colors?

I've got a bunch of old die cast pieces (and a couple of plastic kits) that could use some restoration.  I'm cool with color selecting on original finishing projects or whole rehabs.  But I'm wondering how I can match colors on the pieces that are only small or minor touch ups.  any suggest?  or am I loking at redoing the whole thing if I want the paints to match.  Is there like an old collectors guide that has color references, like they have for automotive restoration?  I know guys can touch up nicks and scratches on the full scale stuff, I'd like to play around with it on some of these old dinged up diecast pieces.

 Kosmonot out