At the nail shop, i notice a small greenish spot under my big toenail. () weeks later it got a tad bigger () no pain. what could this be?

A number of things: The toe nail is tightly adhered to the nail bed most of the time, but slight separations can allow bacteria and fungus to reside there. This is usually not a major issue, depending upon your symptoms. A bacteria known as Psuedomonas Aeruginosa has such a pigment and can show up in a number of places, even a bar of soap. If symptoms presents, simple treatment includes Antibioics and topicals.