Rhubarb Hair Color For bright lights in fair hair. 3/4 ounce rhubarb root 4 cups pure water Simmer rhubarb root in water in a covered nonmetal pot for one hour. After cooling and filtering out solids, apply to the hair as a final rinse, pouring the liquid through again and again. Effects are permanent warm/bright overtones. Red wine may be used instead of water for a warmer tone.