Is green mucus always a sign of an infection?

I had Rhinoplasty 9 months ago and I been having green mucus in my nose is not a lot just, I would say the normal mucus but they are green. what are other causes of green mucus, other than infection? I noticed that they become green if nasal secretions are in my nose for a few days. I went see my surgeon and also another ENT doctor and both said that there is nothing wrong and that green mucus could just be normal. but I have hear that green mucus is a sign of a bacteria infection.