The Lajnah ad-Da’imah stated:
“…If the hair is grey or discolored, it is permissible to dye it any color other than black. If it is of normal color, is not grey, or discolored, it should not be dyed because this would be a kind of deceit and change of what Allah (Exalted be He) has created.”
As well this is the opinion of Ash-Shaykh Albany rahimahullah as can be listened to below in audio form.
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Also, Ash-Shaykh Saalih al-Fawzaan hafidaho-Allah states if it is مشوه meaning it has become disfigured in its appearance then it becomes permissible to dye it.
Note: There is an opinion ascribed to Ash-Shaykh Uthaymeen rahimahullah that states the origin concerning this action is that it is permissible to dye the hair even if the hair isn’t grey or discolored. And there is a third opinion of some scholars which doesn’t state it is haram or halaal but say it is doubtful and it should be avoided.
AbdulFattaah Bin Uthman