If it changes from yellow to white mucus, then it may be an improvement, if it stays white, then it is not, and needs to be clarified by a doctor. If the sputum is yellow and thick at the beginning of the cold and changes to white after a period of symptomatic treatment, it may be a sign of improvement. In the early and middle stages of a cold, the sputum may turn yellow due to viral infection, and then turn white, which means the viral infection has been gradually controlled, and therefore the condition can be initially recognized as improved. If the sputum remains white and thick, it does not indicate improvement. Improvement should be in the form of thinner white sputum or a significant reduction or even disappearance of sputum, rather than the same sputum all the time. If you have cold symptoms, it is recommended that you seek medical advice and treatment under the guidance of your doctor.