Pigment in skin that has lost it

In vitiligo the melanocytes in a patch are destroyed and the skin goes white, and narrowband ultraviolet light is used to coax the surviving cells back. Adding the implant to that light brought colour back faster and more fully than light alone, because the signal that tells a melanocyte to make pigment is being supplied directly. The face and upper body answer better than hands and feet. It works with the light rather than instead of it.