I feel the need to jump in here...I'm a hairdresser and I well tell you that if the color you have now is something you can live with..keep it. Only because if you really mess it up it cost double, triple or more for a professional to do corrective work. If you feel confident in adding low lights to it then go ahead...you don't need to wait any length of time. I would use a semi perm color though. Also...do not use any color with henna in it! Henna stains the hair horribly and there is nothing you can do to get it out without completely frying your hair.