I've argued with people for years about the color of the robots legs. I always thought they were black or faded black while most people thought they were gray. Studio lights, especially with a diffuser, will give them a silvery appearance as they often had. I believe I saw the original legs at the last appearance B9 made in Boston in 1990. Compare the shape and small flaws and you'll see that they match up. What I saw was a black rubber similar to a radiator hose. The middle photo shows this.
It's not irrefutable proof, but I'm fairly certain I'm correct on this. I realize the legs were painted white for the Mystery Island series and were also 23 years old when this photo was taken. Maybe stripping the white paint off changed the color of the rubber. Some color change could have occured while in storage. Maybe they were painted or sprayed with a dull finish for the series, but what I saw was definitely black. I even recall saying, "Oh, they are blacker than I thought." It wasn't painted black either, but a natural rubber look. If you can, look at the View Master photos and what you see is exactly what I saw in person.
It's something to think about.

View Master photos at the bottom of this page:

The legs on the left appear to be sprayed with dullcoat to cut down the glare. The dullcoat evens out the light and makes it appear lighter. It looks like a lightbox or diffuser illuminated it like in the photo below.
One thing is certain - we will probably never know what they really looked like in 1968.