All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad
is His slave and Messenger.
It is permissible to use a makeup pencil or black dye to cover a bald spot or a gap in the beard or chin when needed, on the condition that the dye does not constitute a barrier that prevents water from reaching the skin during ablution, and that it is free of impure substances. This is considered a way of concealing a visible defect.
This does not fall under the prohibition of dyeing the hair black, because that prohibition is specifically related to the hair, not the skin; as the Prophet, sallallaahu 'alayhi wa sallam, said: “Change this (head hair and beard hair) with something, but avoid black.” Narrated by Muslim in his Sahih on the authority of Jabir ibn ‘Abdillah
both.
Furthermore, there is a difference of opinion among scholars regarding whether this forbiddance implies dislikeability or outright prohibition. The opinion adopted on our site is that it indicates prohibition.
Similarly, there is no difference in this ruling between men and women, except for what has been mentioned by some scholars who allowed a woman to dye her hair black if it is for the purpose of beautifying herself for her husband.
Lastly, since you know that plucking the beard is forbidden, you must repent to Allah the Almighty and refrain from doing so. If you suffer from any harm or irritation in your beard or face, you should treat it using medical and therapeutic means.
Allah knows best.