Always do a strand test and an allergy test according to the kit directions before applying any new color to your entire head. Based on the info you provided you could try 3 parts Bright Red and 1 part Black with equal parts developer. Be sure to read the instructions. Resistant grays may take a 45 min. processing time with equal parts color to developer. Then, the last 5 minutes of processing time, take the remaining color developer mixture and dilute by half with water and apply to the previously colored ends.