At one time, many thought that changes in sputum color were a sign of infection. When accompanied by other symptoms, this may be true. There are variables other than illness, however, that contribute to phlegm color. Healthcare providers suggest that allergies, types of foods eaten and the time of day also contribute to various sputum colors.

Bacterial colonies produce a wide range of colors when their numbers reach certain levels. Certain strains of staphylococcus appear yellow, pseudomonas may appear green and serratia colonies are typically clear. These colors may or may not appear in phlegm until an infectious process progresses and is accompanied by many other symptoms. Various sputum colors might be related to irritants or pollutants inhaled in the air or related to the amount and thickness of the phlegm.

Many associate yellow sputum and nasal discharge with the onset of an infection, but this is not the case unless an individual has other symptoms. Yellow phlegm first thing in the morning may be the body ridding itself of old mucus. This is especially true if someone does not see this color in phlegm the rest of the day. Yellow mucus may also be associated with allergies. White phlegm is also not generally a concern unless it is thick and followed by other indications.

Green mucus coughed up first thing in the morning may also be harmless if not seen the rest of the day. In the presence of infection or irritant, white blood cells rush to the area in order to protect the body. Health care providers believe the green color may be the result of an enzyme produced by white blood cells called myeloperoxidase. Fungal infections also typically generate green or sometimes black colored phlegm.

Bleeding in the respiratory tract often appears as blood tinged, rusty or red sputum, and may indicate pneumonia, chronic lung conditions or cancer. This sputum color may also appear after eating or drinking certain foods. This is the case with persons who have recently consumed colas, dark wines or after eating chocolate.