Is it permissible to dye one's beard blond knowing that the original color is black?
Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
Dying hair or beard is permissible with the following conditions:
1. The hair should not be dyed with black colour for the Hadith of the Prophet (Sallallahu Alaihi wa Sallam) who said: "At the last period of this world, some people will dye their hair black, they will not get the smell of paradise." (Abu Dawud)
When the Prophet (Sallallahu Alaihi wa Sallam) ordered to change the grey coloured hair of Abu Qahafah, the father of Abu Bakr, he said: "change the whiteness of the hair, but avoid black."
2. It should be free from the imitation of dissolute persons, polytheists, and Kuffars. The Prophet (Sallallahu Alaihi wa Sallam) said: "whoever imitates a nation he becomes one of them." (Abu Dawud)
If the dye is free for the above prohibitions then it is allowed even if the hair is black.
Allah knows best.
You can search for fatwa through many choices