You can use Ecocolors to deposit on gray hair in between your highlights. Your highlights should be done with care, not to overlap into previously highlighted hair. The highlights should be done with a mild developer when using bleach(10 or 20 vol) . Studies have shown that using 30 or 40 with bleach does not work any faster and only damages the hair shaft. We recommend highlights redone every three to six months depending on the amount of highlights that are done .