Firstly: 

It is makrooh to pluck grey hair from the head or moustache, because of the hadeeths narrated from the Prophet (blessings and peace of Allah be upon him) concerning that, such as: 

The report narrated by at-Tirmidhi from Ka‘b ibn Murrah (may Allah be pleased with him) who said: I heard the Messenger of Allah (blessings and peace of Allah be upon him) say: “Whoever has one hair that turns grey in Islam, it will be light (noor) for him on the Day of Resurrection.”

Classed as saheeh by al-Albaani in Saheeh at-Tirmidhi

In Musnad Ahmad and Sunan at-Tirmidhi (1635) it is narrated from ‘Amr ibn ‘Abasah (may Allah be pleased with him) that the Messenger of Allah (blessings and peace of Allah be upon him) said: “Whoever has one hair that turns grey for the sake of Allah, it will be light for him on the Day of Resurrection.”

Classed as saheeh by al-Albaani in Saheeh at-Tirmidhi. 

Al-Bayhaqi in Shu‘ab al-Eemaan narrated that ‘Abdullah ibn ‘Amr (may Allah be pleased with him) said: The Messenger of Allah (blessings and peace of Allah be upon him) said: “Grey hair is the light of the believer; no man turns grey in Islam but for each grey hair he will have one hasanah and he will be raised in status one degree.” 

Silsilat al-Ahaadeeth as-Saheehah, 1243. 

It was narrated that Abu Hurayrah (may Allah be pleased with him) said: Do not pluck grey hairs, for they will be light on the Day of Resurrection. Whoever has one hair that turns grey in Islam will have one hasanah for each grey hair and he will be raised one degree.” Narrated by Ibn Hibbaan. al-Albaani said in Silsilat al-Ahaadeeth as-Saheehah (3/247): Its isnaad is hasan. 

Ibn ‘Adiy, and al-Bayhaqi in Shu‘ab al-Eemaan, narrated that Faddaalah ibn ‘Ubayd (may Allah be pleased with him) said: The Messenger of Allah (blessings and peace of Allah be upon him) said: “Grey hair is light on the face of the Muslim, so whoever wishes, let him pluck out his light.

Silsilat al-Ahaadeeth as-Saheehah, 1244 

These hadeeths indicate that it is makrooh to pluck grey hairs, whether from the head or the moustache. 

But if the grey hair is in the beard, it is haraam to pluck it. 

Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) was asked: What is the ruling on plucking grey hair from the head and beard? 

He replied: With regard to the beard or facial hair, it is haraam, because this comes under the heading of namas which refers to plucking the facial hair, and that includes the beard. It was proven that the Prophet (blessings and peace of Allah be upon him) cursed the woman who plucks facial hair and the one who has that done. And we say to this man: if you were to look for every hair that has turned white and pluck it, you would have no beard left, so leave what Allah has created as He created it and do not pluck anything. 

But if it is plucking hair from the head, that does not reach the level of being haraam because it does not come under the heading of namas. 

End quote from Majmoo‘ al-Fataawa, 11/123 

And Allah knows best.