Yes, I have had this experience. About 6 months ago when my son was 2.5 he fell and hit his lip. Sometime after that, his front tooth started turning a darker color. I took him to the dentist, and his was turning more of a yellowish color, as opposed to grey, but she did tell me at that time, that they prefer to see them turn the yellowish darker color as opposed to the greyish darker color. They did xrays, and said it didnt look like there was any root damage or damage to the adult tooth, but that I had to bring him back in a month for another xray. That one still looked promising, so then we went three months. So far, his tooth has been salvageable, but she said that the concern is making sure that the adult tooth and root remain salvageable which is why they want to xray it and check it. If they felt that the baby tooth was an issue, they said they would have to take it out in order to save the adult tooth behind from being affected. She also told me to look every day when I brush his teeth for little white "blister or pimple" looking things along his upper gum/ lip and to call her immediately if we did, as that indicates an abscess and is dangerous. I would definitely get her into the dentist for an xray so they can start monitoring it. They explained that the reason it turns color like that is just from the bruising/ bleeding that occurs behind the tooth and goes down into the tooth....and quite often it will get better with time...(my sons has turned whiter over time)- but its better for them to be able to monitor it from the beginning. Unless there is serious damage, chances are they will just do an xray and watch it for the next 6 months or longer.