Pleurisy is an inflammation of the pleura, the double-layered membrane that surrounds each lung and the rib cage. The double-layered pleura protects and lubricates the surface of the lungs as they inflate and deflate within the rib cage. Healthy pleura have a thin, fluid-filled space between the two layers that lets them glide gently across each other. When they become inflamed, the diseased surfaces rub painfully together. This causes a characteristic sound called “friction rub.”
Pleurisy cases are defined as having pleural effusion or as being dry. Pleural effusion, an accumulation of fluid in the pleural space, is more common, and is essentially a side effect of numerous diseases or trauma. Dry pleurisy refers to cases where there is no fluid build-up. Pleural effusion is less painful due to the fluid forcing some separation of the membranes. However, the fluid puts pressure on the lungs which can lead to respiratory distress and even lung collapse.
We cannot say why the color is green but infections can cause green discharge. As to what color could mean cancer, we cannot say - exams, scans and biopsies are used to diagnose cancer, not the color of fluids.
Your friend will need to discuss this with her oncologist or see a lung specialist.