black dye

Q:

1. What is the Shar'ee ruling regarding hair dye? Is it permissible to use?

2. What colours of dye should one use and which colours should one avoid using?

3. Is there any difference in the ruling between men and women?

4. Is it permissible to use hair dye which is non-porous and prevents the water from touching the hair? If one used such dye, will one's wudhu and ghusal be complete?

5. I heard that applying mehndi is a Sunnah. Can a person dye his beard or hair with mehndi and will one receive the reward of the Sunnah if one applies it?

Q: Black hair dye is prohibited. Is there such a thing as black mehndi for hair? If so, is that allowed?

Q: What is the masala regarding black mehndi on hair for both men and women. Is it allowed to cover white hair?