Marti

Even without seeing the photo, I could tell you that you have aquired a Pseudomonas Bacterial infection on top of the nail plate. this is the direct result of the nail technician not properly prepping the nail plae. leaving cracked product on the nail plate and applying right over it. All this does is seal bacteria between the nail plate and the overlay, resulting in infection. You did the right thing to take off the overlay. Simply exposing the infection to the air will allow the nail plate to dry out. The bacteria needs the moisture to grow, so keeping it dry for a few days will 'kill' the infection. I might suggest wiping the nail with a pad dampened with alcohol. Do this especially after having your hands in water, taking a shower, etc.

You can lightly buff the surface of the nail to remove some of the stain, but most of it will remain and grow out with the nail plate. The stain is a by-product of the infection and is compromised mainly of iron compounds.