Hi Dear , As per your query you had cold and now you have black substance in nasal discharge , you alsso haave habit of smoking . Well there can be many reasons for the symptoms you mention in query like :- - dust - smoke - environmental Hazards like coal mine - infection - blood from busted blood vessels . But in your case it seems to me that black substance is due to smoking habit or infection sinusitis or upper respiratory track infection . I would suggest you to consult ENT specialist for proper diagnosis . Doctor may order certain test like throat swab test , viral culture test , CT scan and physical examinetion . Doctor may prescribe antibiotics at least for a week along with decongestant and may recommend tonsillectomy . For now quit smoking , do warm saline gargles and saline nasal rinses . Hope your concern has been resolved. Get Well Soon. Best Wishes, Dr. Harry Maheshwari