A person with a green fingernail is suffering from a condition called green nail syndrome. This infection leads to discoloration of the nails, usually referred to as chloronychia.
The discoloration may vary from one person to another and it usually occurs underneath the nail. Therefore, scrubbing and washing may not help in removing the color. In most common cases, the condition occurs on one or two nails, either on the toenails or fingernails. It is usually caused by a bacteria referred to as Pseudomonas aeruginosa. If treatment fails, the nails may need to be removed, as stated by American Osteopathy College of Dermatology. A doctor can prescribe an oral antibiotic, such as ciproflaxin, for this condition.