Thanks for asking the query,
Black colour discolouration in the mouth can be due to poor oral hygiene
and calculus deposition, chronic use of tobacco.
Loss of sense of taste can be due to poor oral hygiene, infections, nutritional deficiencies, immunological disorders.
I would suggest you to visit to an Oral and Maxillofacial Surgeon and get the checkup done.
Go for symptomatic treatment of complete mouth scaling and polishing.
Maintain a good oral hygiene, use antiseptic mouthwash gargles twice daily.
Take a balanced diet, drink lots of water and keep yourself hydrated.
Hope this helps out.