I am from a younger generation where star wars (episode 4-6 and I was born shortly before episode 1) and I do remember him having one leg as slightly discolored to his other. That being said, in most scenes of episode 4 you see C-3PO in the desert of Tatooine where much of the set would reflect off of it making it look like the rest of his body but more dull (see below)

So while I wouldn't have thought his leg was silver, I did notice it was a different color.