The color of pleural effusion is also related to its nature. In leaking fluid, the color of pleural effusion is mostly pale yellow, or sometimes even colorless leaking fluid. In exudate, most of it is also pale yellow, sometimes straw yellow, and even some pus pleural effusions are cloudy in color. In addition, there are some bloody pleural effusions. The color of bloody pleural effusions can range from light to dark, light is light bloody, such as the color of washed flesh water; dark like the color of drawn blood, and even can be grass green or black, which is actually related to the cause of the pleural effusion. Pale yellow or grass green often suggests that the cause of the exudate is tuberculous pleurisy or pneumonia. Hemorrhagic pleural effusions are most commonly malignant pleural effusions, but they also include some tuberculous pleurisy, pulmonary embolism, etc. In conclusion, the color of pleural effusion is related to its etiology.