Is it permissible for a man or a woman to dye and remove gray hair?

All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

Dyeing the hair with a color other than black is permissible for men and women. It is narrated on the authority of Jaabir that Abu Quhafah (Abu Bakr's father) was brought on the day of the Conquest of Mecca, and his head and beard were white like "Thaghamah" (a plant whose flowers and fruit are white). The Messenger of Allaah, sallallaahu ‘alayhi wa sallam, said: "Change this with something, but avoid black." [Muslim]

However, plucking out white hair was forbidden by the Messenger of Allaah, sallallaahu ‘alayhi wa sallam. ‘Amr ibn Shu‘ayb related from his father on the authority of his grandfather that the Prophet, sallallaahu ‘alayhi wa sallam, said: "Do not pluck out any white hair, for it will be the Muslim's light on the Day of Judgment." [At-Tirmithi and Ibn Maajah]

Allaah Knows best.