what is color of cough
Green or Dark Yellow Phlegm. A thick and dark yellow phlegm may be a sign of a viral or bacterial infection, sinus infection, or lower respiratory tract infection. Typically, this occurs when the immune system sends white blood cells, known as neutrophils, to the area of infection.his causes the mucus to stagnate and dry out, leading to a white discharge. Meanwhile, coughing up gray phlegm may be a sign that the body is trying to get rid of resins or tars that accumulated from excessive smoking or inhalation of large amounts of air pollutants like smog or dust.