It is considered to be a longevity herb. Sage leaf is also used to restore hair color. This one is taken internally also. Though it can also be used as a hair rinse to speed up the process. A lack of copper can lead to premature graying, though too much copper can also cause problems, so watch your intake.
B vitamins are also important for healthy hair.
A good B complex should do fine. Phenylalanine is required for hair pigment formation. Though if you have high blood pressure or PKU I would suggest using tyrosine instead, which is produced in the body from phenylalanine. These are amino acids and as with all amino acids they should be taken on an empty stomach. Other wise their absorption can be interfered with or blocked by other amino acids that are present.