How can one tell the difference between silver wire and aluminum wire?

I recently processed a big old old auto diagnostic machine which had some insulated copper wire and some insulated silver COLORED wire. The technology in the machine would date it to the 70's? There were several circuit boards with silver fingers at the plug in sites.

On a side note - I believe some circuit boards have some of the wet axil silver tantalum, umm, things. (Can't remember the name at the moment.)



I'll try to remember to take some pictures of the boards and post on this thread.