If the dark brown isn’t dark enough, try using dark ash brown or mixing dark ash brown and black. Depending on the thickness and strength of the cuticle layer of your hair, you may need to go darker. Some ways to encourage deposit is to leave the color/ developer mixture On with a cap and heat for 45 minutes. Doing a strand test and an allergy test is the only way to know which tone is best for you and how long you need to let the color process.