the colour of sputum changes for white to green in the spitoon ( container) after some time why what does it indicate.

The colour or sputum can indicate different pathological disease processes and can differentiate between them, such as pneumonia, tuberculosis, a cold, and other upper respiratory tract infections.

It best indicates that it became infected. Mucus is clear or white when there is no infection present.. and is yellow or green when there is an infection present.