My daughter had similar thing happened to her milk tooth. It had turned grey for a some time and the pediatrician dentist told us to leave it to fall out on its own. 6 months later it was still there and looking really bad. She was 9 then. Finally, I took her to a regular dentist and when he picked it out, it came out in 5 little pieces. The nerve has been dead for a long time and the only thing holding it in is her gum. It was also interfering with the growth of her adult tooth by being there. So for me, if I ever see a grey tooth that look suspicious, I will get a dentist to see it and decide then.
I have recently noticed the DS tooth is going grey. He recently fell while dancing so wondering if he killed the nerves. Would like to see a dentist to ensure no infection or damage to adult tooth. We live in DSO as of today! Any recommendations would be appreciated.