Buy Goldwell Hair Color Permanent - Goldwell Topchic Hair Color Coloration (Tube) 2N Black. How-to-Use: Recommendation: Perform a preliminary patch test according to the following directions prior to each application, even if the client has had color treatments before. Using a cotton-tipped applicator, apply the color mixture to a 1 x 1 patch of clean skin (gently wash with mild soap and water) on the inside of the forearm and leave to process. After 45 minutes, cleanse th