Using henna or dyeing gray hair is permissible and it is part of the Sunnah of the Prophet (peace be upon him). It is allowed for men to dye their gray hair on their heads and their beards. Abu Hurairah (may Allah be pleased with him) narrated, “I heard the Messenger of Allah (peace be upon him) saying: “Jews and Christians do not dye their hair, so act differently from them.” (Agreed Upon)
On the other hand, dyeing gray hair with black is prohibited. Jabir narrated Abu Quhafah, father of Abu Bakr (may Allah be pleased with them) was presented to the Messenger of Allah (peace be upon him) on the day of the conquest of Makkah and his head and beard were snow white. The Messenger of Allah (peace be upon him) said, “Change it (i.e., dye it) and avoid black color.” (Muslim)
Coming to the ruling of applying henna on one’s hand or nails, the majority of scholars are of the view that it does not invalidate one’s ablution unlike the nail polish that must be removed before offering wudu’ (ablution).
For more information about the ruling of dyeing or using henna, watch this short talk with Dr. Muhammad salah.
Source: Huda Youtube Channel.