Changing hair
    colour and “relaxing” the hair
Question

                I have seen that some people use
      materials to dye their hair different colours, be it black, red, etc., and also using
      something else to make curly hair straight. It is permissible to do such things, and does
      the ruling apply equally to young and old?
Praise be to Allah.There is nothing wrong with changing the hair colour and dyeing it any
    colour, except black. There is also nothing wrong with using something to make curly hair
    straight. This ruling applies to young and old alike, so long as no damage results from
    doing this and the material used is pure (taahir) and something that is allowed in Islam.
    However, dyeing the hair pure black is not allowed for men or women, because the Prophet
    
 (peace and blessings of Allaah be upon him) said: “Change this grey hair, but
    avoid black.” (Fataawa al-Lajnah al-Daa’imah, 5/168).