Ya - that is a tough one if there are not any other symptoms to his nose it could be so many things causing extra sinus discharge .... specially this year when our weather has been so WEIRD this winter and not have had enough below freezing for long enough periods to actually 'kill off' the spores and crap outside as a result many people are experiencing their worst 'allergy season' in their life time as it is starting earlier and way more concentrated

Children who are teething also have runny nose syndrome as well and while normally 'clear' it too can change color for seemingly benign reasons.

The color of your mucus can change for various reasons ... while yellow and green mucus is typically stated to be indication of 'cold' or 'infection' in the absense of any 'other' symptoms of infection the cause my not be infection at all - I have read online that the processing too many environmental toxins and allergens through your sinus can cause changes in the color of our boogers in a perfectly 'healthy' person so in the absence of any other symptoms to indicate 'cold' I would assume this is just an allergen and poses no contagious issue to the others.

However that said would still suggest that the child's DR follow up with WHY the excessive drippage...if it is allergies perhaps allergy tests to identify WHAT so if possible it can be eliminated from his diet or environment and if not able to omit exposure allergen medication to reduce the symptoms for him?