It doesn't turn yellow under normal circumstances. Unless you are in an epidemic area and you have been there for more than 4.5 hours. The health code will turn yellow, indicating that you belong to the key population of epidemic prevention and control, including confirmed cases or asymptomatic infected people.
Yellow code personnel receive COVID-19 nucleic acid detection twice within 3 days (24 hours apart). After all the results are negative, the yellow code can be changed to green code (Yuekang code is automatically retrieved in the background).