Almost all of us have experienced productive cough, which may be because of a common cold, bronchitis, or other respiratory tract infections. Coughing up phlegm is rather a good sign, as accumulation of the same can lead to chest infections and other medical complications. Nevertheless, a chronic cough condition with phlegm that is discolored (yellow, rusty-brown, green, etc.) should not be neglected, as it can be a symptom of some serious lung ailments.