Jaabir ibn ‘Abdullah reported that Abu Quhaafah was brought on the day of the conquest of Makkah, and his head and beard were white like “thaghaamah” (a plant whose flowers and fruit are white). The Messenger of Allah (Peace & Blessings of Allah be upon Him) said: “Change this with something, but avoid black.” (Reported by Muslim, no. 3962).
Ibn ‘Abbas (may Allah be pleased with him) said: “The Messenger of Allah (Peace & Blessings of Allah be upon Him) said: ‘At the end of time there will be people who will dye their hair black like the crops of pigeons. They will never even smell the fragrance of Paradise.” (reported by Imam Ahmad, see also Saheeh al-Jaami‘, no. 8153).
It was also reported from the Prophet (Peace & Blessings of Allah be upon Him) that one should change grey hair, using any colour except black. Abu Dharr reported that the Prophet (Peace & Blessings of Allah be upon Him) said: “The best things with which to change grey hair are henna and ‘katam’ (a plant similar to henna which is used as a dye).” (Reported by al-Tirmidhi, no. 1675; he said: This is a saheeh hasan hadith).
Dyeing hair with pure black dye is haram because the Prophet (Peace & Blessings of Allah be upon Him) said: “Avoid black,” and because of the threat of punishment reported with regard to this matter. This ruling applies to both men and women.
But if the black dye is mixed with another colour, so that it is no longer black, there is nothing wrong with it.