@healthybon After years of bronchiectasis I have noticed a pattern when mucus color changes. I could be wrong but my suspicion is that an overnight change in mucus color can be due to reflux/GERD. One day things are yellow. Next day first few huffs are greenish.

If you have not watched Medical Management of GERD with Dr. Huitt, please watch it. The lungs and stomach lie in close proximity and it's common for us to aspirate and have reflux events many times a day. The average number is 30, even in healthy people! Add in lung disease those aspirations from digestive acids can cause chemical burns to the trachea and sinus area, and you develop green phlegm or the beginnings to an infection. Of course, it's also possible to have some other infection brewing but if it's an overnight change, review your reflux/GERD precautions.