Generally, if you want to change your hair color, you need to have your hair dyed. Constantly coloring your hair can lead to stripping and damaging of hair that only makes it weaker over time. If you want to go the non-chemical route, you can take Melancor. This is a supplement that allows the melanin in the pill to combine with your hair's natural melanin that gives it its color. When the two combine, hair cells become revitalized and natural color begins to come back and replace the gray.
Swallow the Melancor pill whole; do not crush it. Melancor forces melanocytes to increase your body's natural formulation of melanin pigments. It also prevents DHT from hindering the growth of hair follicles, which also leads to gray hair.
Take two pills twice daily. You should take them either during or after meals. You need a full stomach so that the pill does not make you nauseous.
Follow the instructions on the bottle, and consult a physician if desired results are not achieved, or if you are having reactions to the supplement.