A: Yellow nails are generally caused by not using a base coat when using a very dark color of polish. I've had instances when even using a base coat didn't help and my fingers glowed with yellow after removing a very dark color.

There are base and top coats designed specifically for avoiding the yellow nail. One is called Yellow-Out. It's a top coat, and you can find them at most national drug stores like Rite Aid or CVS.

A home-made remedy is to use a Q-tip dipped in hydrogen peroxide (you can find this at any supermarket or drug store) and rub on nails (try to avoid the cuticles) once or twice a day until the nail lightens. It should take about a week.

Hope this helps!