I have an infection in my incision & pus was yellow but it changed to green. What does green signify?

Infection. That usually means you are getting an infection in the incision. Please see your doctor as soon as you can. In the meantime keep changing the bandages, so you can tell if it is getting worse. If it is please go to the emergency room after calling your surgeon.
Green puss. Green pus is due to infections with psedomonas aeroginosa, in the incision wound.Itis green dueto antibacterial proteinproduced by some white cell, it is callled myeloperoxidase you should have it looked at and get culture taken and get treated appropriately by your doc.
Pseudomonas? It means you need to inform your surgeon. Anytime, there is any change in an appearance of a wound your surgeon should be notified. Green is a color that is often attributed to a pseudomonas infection which is a type of bacteria. It might mean your doctor may have to change your antibiotic or add an antibiotic. (assuming no further procedure such as the surgeon cleaning the wound more is necessary.