Go for xray to determine the cause

Share some clear photographs of the effected tooth. Maybe it's carious or deposits on that tooth. Consult with doctor online or offline for better guidance and treatment options.

It is probably a stained tarter. Worst case it can a decay of teeth. You must consult your nearby dentist at first.

Firstly you need to share the pic of that particular tooth so that we can guide you accordingly and it will b better if you could consult the dentist directly so that the correct diagnosis can be made and treated accordingly. The color changes of tooth can be due to many reasons like staining, cavity, or deep caries approaching to pulp and making that tooth dead.

Colour change in tooth is mostly due caries or due to any trauma caused to teeth previously.

Hello dear Please be calm I think change in colour is due to dental caries or gingival stains.i suggest you to share pic for confirmation of diagnosis.for further information you can consult your Thanks

You should either consult online or visit a dentist, color change might be due to developing caries.

Check the dentist ur nerve supply to the tooth is cut