Holy crap, you aren't kidding about those sizing beads being huge! Mine are less than half that size.
With the stones being grey, it's possible that some solder got left on the back of the stones during the work. That happened to me when I was having my jeweler fix some issues I had with my engagement ring, before it was finalized. They gave it to me and I kept seeing this dark spot where a stone should be. I would have a mini-heart attack everytime I saw it because the stone was there but it was so dark it looked like it had fallen out. I took it back to the jeweler to point it out and she told me the solder hadn't been cleaned from the back of it. She was able to have it fixed and it's fine now. Maybe that's what happened to your stones.