Don't know if this is any help but have found this quote on www.ds-health.com/nose.htm....
" The fun starts when the mucus isn't clear. Almost all doctors agree that cloudy or white nasal mucus indicates a head cold, caused by those nasty viruses that linger in schools, daycare centers and Sesame Street concerts. (Please note that wind, cold weather and running outside with wet hair and bare feet do not by themselves make a child sick.) Head colds may last 5 to 7 days, and typically cause some mild chest congestion before disappearing completely.
What about the yellow or green stuff? Actually, most doctors call this "purulent drainage" but it doesn't necessarily mean anything more than infection. Viruses can cause the mucus to be green or yellow. After a certain amount of days, then doctors might call it "sinusitis" or "upper respiratory infection" and prescribe antibiotics. How long is that time frame? It depends on the doctor, and that depends on the last thing they've read or how sick the child is. Without fever or any other problems, most doctors tell parents to wait 3 to 7 days after the emergence of the yellow/green mucus before prescribing antibiotics. One thing to keep in mind, by the way, is that nasal mucus typically looks dark when dried or in the first 2 hours of the morning, so that doesn't count. And mucus that changes from clear to discolored and back is most likely a virus."