"I'd like to dye my white hair roots to maintain the same color."
"How to Dye White Hair Roots. Your white or gray hair may only be visible at the roots, but you still feel its appearance mars your attractiveness. Hair turns gray when the melanin contained in the hair follicles stops producing pigment. Rather than dying all of your hair, you can apply natural henna dye just at the roots." [Ehow.com]
"Mick Jagger's secrets for staying youthful. Unlike many of his peers who let their gray or white hair show, Mick has his hair dyed by a private colorist to maintain the same hair color." [The Examiner - USA]