So far as I know, electrolysis is it for gray colorless hairs.
The laser needs to put out light that will be absorbed by the hair follicle and not by surrounding tissue, so it transfers energy to the follicle, killing it, without harming the other tissue. A gray hair has no coloring, that is, it doesn't absorb selected colors like black, brown, or red hairs do. With colored hair, a laser can be tuned to emit a color the hair will absorb while minimizing damage to other tissue.
I wish it were otherwise. I REALLY wish it were otherwise.