Dark brown mucous from my throat. i do not smoke and my exposure to pollutants is average. i do not feel any other respiratory issue. please help.

Blood?..: Brown colour may actually come from broken down blood, ie. Hemosiderin. Gums, throat, coughing, sinus cavities can all be a source. This is the most common cause, other than inhaling dust, etc. This can be easily checked by taking a specimen and having it examined for this causes.

? infection: Though you may not feel it, dark brown mucus suggests either an infection or some old blood in the mucus. Would have it checked out.