Hello. welcome to HCM.
green and colourless discharge from the nipple is commonly indicative of a duct ectatsia i.e. a condition in which one or more ducts dilate and discharge pent up secretions. The condition can be stagnant or be aggravated in future. So you need to be examined and treated. There are both medical and surgical treatment
options available, decided according to individual patient. Make sure there is no lump on self examination and plan a visit to a specialist in the near future.