Don't lose hope yet! DD bumped into DS on the trampoline and 3 weeks later her tooth started going grey - I was heartbroken!
One of the other mums (whose boy had a bad mouth incident and lost one totally) said not to panic yet because it might be ok. When her boy hurt himself one came out, the other went dark but seemed to recover.

And that's exactly what happened to DD! After a few months it's ok again, the right colour came back and you can only tell if you look really really hard.

hth