Ruling on using herbs to dye the hair that give it a deep black colour
Question

                I have heard about dyeing the hair with natural herbs. I am going to get married, and I want to dye my hair in order to beautify myself for my husband. But I heard that these herbs give the hair a deep black colour; my hair has a few white hairs in it. Is using these herbs in a case like mine permissible or not? Please note that I wear niqab.
Praise be to Allah.
    Firstly: 

    There is nothing wrong with using natural herbs to dye the 
    hair or for other permissible purposes, so long as there are no harmful 
    effects, because Allah, may He be exalted, says (interpretation of the 
    meaning): “He it is Who created for you all that is on earth” [al-Baqarah 
    2:29]. 

    Secondly: 

    It is not permissible to dye the hair black, for men or 
    women, young or old, because of the general meaning of the evidence which 
    indicates that that is not allowed. 

    The scholars of the Standing Committee for Issuing Fatwas 
    were asked: I have seen some people using something to change the colour of 
    their hair, whether they make it black or red, and I have seen them using 
    something else to straighten curly hair. Are any of these things 
    permissible? Do young people come under the same ruling as old people? 

    They replied: There is nothing wrong with changing the colour 
    of the hair to any colour except black or with using something to make curly 
    hair straight. The ruling is the same for young people as for old people. 
    That is so long as there are no harmful effects and the substance is taahir 
    (pure) and permissible. 

    With regard to changing the colour to pure black, that is not 
    permissible for men or women, because the Prophet (blessings and peace of 
    Allah be upon him) said: “Change this grey hair, but avoid black.”

    End quote from Fataawa al-Lajnah ad-Daa’imah, 5/168 

    Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: If 
    the hair is dyed black, the Prophet (blessings and peace of Allah be upon 
    him) forbade that when he enjoined changing grey hair but avoiding black, as 
    he said: “Change this grey hair, but avoid black.” 

    There is also a stern warning addressed to the one who does 
    that, which indicates that it is haraam to change the hair to black. As for 
    changing it to other colours, the basic principle is that that is 
    permissible, unless it is done in the style of disbelieving or immoral 
    women, in which case it is haraam from that point of view, because the 
    Prophet (blessings and peace of Allah be upon him) said: “Whoever imitates a 
    people is one of them.” Narrated by Abu Dawood, 4031; classed as saheeh by 
    al-Albaani in Irwa’ al-Ghaleel, 5/109.

    End quote from Majmoo‘ Fataawa wa Rasaa’il Ibn ‘Uthaymeen, 
    11/120 

    What is meant by the warning is the words of the Prophet 
    (blessings and peace of Allah be upon him): “At the end of time, some people 
    will dye their hair with black like the crops of pigeons. They will not even 
    smell the fragrance of Paradise.” Narrated by Abu Dawood, 4212; an-Nasaa’i, 
    8/138; classed as saheeh by al-Albaani in Saheeh al-Jaami‘, 8153. 

    Thirdly: 

    It is permissible to use the herbs mentioned to straighten 
    hair, but if they give a deep black colour, it is not permissible to use for 
    one who has some grey hairs. 

    Shaykh Ibn Baaz (may Allah have mercy on him) was asked: Some 
    people use a mixture to straighten the hair; this mixture is composed of 
    henna and a number of other herbs, which includes a herb that dyes the hair 
    black. What is the ruling on using this mixture? Please note that they are 
    using it for the purpose of straightening the hair and not to dye it black, 
    because some of them have black hair. What is the ruling on using it for a 
    woman whose hair is black but there are some white hairs that are not due to 
    old age, and she is also using it for the purpose of straightening her hair? 
    Please advise us concerning that, may Allah reward you with good. 

    He replied: 

    There is nothing wrong with using the paste mentioned to 
    straighten the hair if the woman who is using it does not have any grey 
    hairs. But when there are grey hairs, it is not permissible to use anything 
    that will turn the grey hairs black, because the Prophet (blessings and 
    peace of Allah be upon him) said: “Change this grey hair, but avoid black.”

    End quote from Fataawa ash-Shaykh Ibn Baaz, 10/63 

    Based on that, if these herbs dye the hair black, and make it 
    deep black as you say, then you should not use them.

    And Allah knows best.