The Cleveland Clinic website offers a phlegm color chart that highlights the different colors of mucus and their possible meaning. Nasal mucus alone is not used for diagnosing a disease, but doctors use it to determine what happening in the nasal passages, states Cleveland Clinic.
The colors of mucus include clear, white, yellow, green, and pink or red, notes Cleveland Clinic. Other colors are black and brown. Clear means normal, as it's water that contains antibodies, dissolved salts and proteins. White indicates congestion and can be a sign of a cold or nasal infection. Yellow shows that an infection is progressing, and green means that the immune system is fighting the infection. Black can be an indication of a severe infection.