Is There Any Treatment to Darken Gray or White Hairs to Improve Laser Hair Removal Treatments?

I agree with my colleagues that changing the hair color does not fool the laser beam that will only see the dark hair at the root. The gray hair might need to be treated with electrolysis ( if you can find someone who still does this)

Lasers create a beam of highly concentrated light that penetrates deep into the skin where it delivers a controlled amount of therapeutic heat. This light energy is absorbed by the pigment located in the hair follicles. Darkening your hair does not change the pigmentation at the level of the hair follicle and will have no effect on improving the result of your laser hair removal treatment.