Dye and Mehndi

Hair dye

Q: I want to ask that if I dye my hair using ordinary dying agents available in the market, would it be an obstacle for my wudhu? Moreover, is it permissible to use dye in black colour?

Using black dye

Q: I am a 21 year old girl and my original hair colour is black, last year I did colour it blond and now its looking bad like two hair colours. I am also married. I heard that its not allowed to colour hair black in Islam. Is that true? If yes then why? I just want my natural hair black and I can't trim it either.