Does the health code become black and white when it becomes invalid?

The normal health code is green. If you have been to an epidemic area, the health code will turn red. But sometimes when we open the health code, we will find that the health code becomes black and white. The health code became black and white, probably because it has not been used for a long time. As long as you refresh the health code, it will turn green again. Therefore, the health code should be refreshed regularly. In order to keep the normal color.