9 year old recovering from a cold. face very pale but otherwise looks like covering well. why does this happen and how long to get colour back?

Doctor can check: People shouldn't look pale when recovering from colds or other minor viral illnesses. If a person looks pale compared to usual, and has few or no ill symptoms, her doctor can take a look, do an exam, and perhaps check a blood test to make sure there is no anemia. Sometimes viral illnesses can cause a drop in blood count for a while. Most of the time, that doesn't happen.