Picture of Discoloration of Nail Plates
The nails are susceptible to discoloration by a variety of agents. Potassium permanganate is known to stain nails a brownish-purple color. Silver nitrate will turn the nails black. The pictured stains are due to resorcinol. Nail stains may not look very nice, but they are not dangerous.
Text Reference: "Discoloration of the Nails: Concomitant Use of Nail Lacquer with Resorcinol or Resorcinol Monoacetate (Euresol) as a Cause." AMA Archives of Dermatology.