@dianajc On a CT scan mucus plugs appear white in our breathing tubes, which are filled with mucus. The black areas are where there is air. Mucus plugs like to reoccur due to the nature of bronchiectasis. That's why we're encouraged to clear our lungs twice a day so mucus does not continue to build up forming more and more mucus plugs. When coughed out they can appear as thick, solid or a rubbery sticky mass varying in color (clear, white, gray, yellow/green, brown or blood-streaked).