I have a 94 Deville with the "gold" looking mirror on the drivers side. When it is cold outside, the mirror fogs up. The normal looking mirror on the passenger side doesn't do this. I noticed a small spot in the gold coloring that looks worn off. Could that have anything to do with it?

It is the auto dimming (electro-chromatic) function of the mirror that you are talking about and it has failed. Time for a new mirror. Ebay is your friend. The glass is replaceable if you can find it. There is a similar thread in the Seville/Eldorado section.