If your house is really old (pre-WWII), it's possible that you have copper wire that has been tinned -- with an overcoat of tin/lead, to make it easier to solder. In this case, the wire will have a silver/gray color, but if you look at the cut end of the wire it will show the copper core.
For a short while there were some installations that used copper-clad aluminum which was an aluminum wire with a copper overcoat. In this case, the wire will appear reddish, but the cut end will reveal a silver/gray/ core.
So the moral of the story is to be really sure what you have, you have to look at a cut end of the wire.
The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.