If this discolouration is associated with the lifting of a nail coating from the nail plate it is probably ‘greenies’ or chloronychia all of which are a bacterial infection of Pseudomonas. Please see the full article on the condition chloronychia
Proper Treatment and Recoating After Nail Infections
In any case, the way to go is to remove the coating and seek medical advice. Once a correct diagnosis has been established, then a range of therapies are available which include avoidance of moisture, topical acetic acid/hypochlorite soaks (vinegar/bleach), antibiotics, and others.
The doctor will be able to prescribe the most suitable one. Only apply a new coating once the treatment has been successful, the infection detained, and the “greenie” has grown out.
