We recommend you do a strand test with a drop of color and a drop of developer. Apply with a Q tip to a gray area. Let it process 30-45 minutes.Then shampoo, dry and determine if you like the color and/ or if you need a longer processing time. A 45 min. processing time is recommended for resistant gray hair. You can recolor immediately if you saw no coverage. DO A STRAND TEST to be sure you like the end result.