When you have phlegm and spit it out sometimes it is green and suddenly changed to white Why did it change color?

The color of phlegm can change based on the presence of different substances, such as bacteria, viruses, or immune cells. Green phlegm often indicates a bacterial infection or the body's response to an infection, where white blood cells are involved in fighting off pathogens. As the infection resolves or if the body clears the mucus, it can turn from green to white as the number of immune cells decreases. Other factors like hydration and air quality can also influence the color and consistency of phlegm.