It’s totally safe to use oVertone on keratin treated strands. Keratin treatments are reparative and will help heal (close) the cuticle of your hair. A closed cuticle can act as a door, shutting out the pigments. Since oVertone doesn't lift or lighten and contains no harsh chemicals, a slightly-open cuticle is ideal for the best color results. For this reason, we highly recommend coloring your hair with oVertone before using any reparative treatment. That way, your hair can accept the pigments and produce a more visible color payout!