What does dark green phylegm mean?

Dark green phlegm: It may mean chronic bronchitis from cigarettes smoking. It may represent acute bronchitis or pneumonia if associated with other symptoms like high fever, chills, rigors, shortness of breath, chest pain etc. Are you a cigarette smoker and do you have other symptoms. Need further evaluation by physician or lung specialist.

Depends: The most common reason for this is a virus that causes acute bronchitis. 10% caused by bacteria. It is very worrisome if you have an underlying lung disease, copd, for example. Shortness or breath or fever (especially a late fever rather than the first few days of the illness) is also bad. Late fever is always a reason to go to the doctor right away. Any fever over 65 would also be worrisome.