Valley of the Dragons (1961)?
well, that happened to me tonight while I was watching the interesting Creation of the Humanoids (1962). right at the beginning of the movie this "robot" shows up. pretty spiffy looking, huh? nice and shiny silver, very sleek.
however, it started as an alien from 1956's Earth vs the Flying Saucers. and since I have actually seen and touched one of the remaining suits (in 1981... it was a World Con in Denver called Denvention II) I know they weren't silver to begin with.
I like these surprise cameos.