If you have dark hair, then you need to bleach your hair before dying it blue. If you already have a color in your hair, you may need to use a color remover to get your hair back to its original color. Black hair will most definitely require bleaching, but a lighter brown may not. It’s possible to get away without bleaching your hair first if you have a lighter hair color, however, it might not turn out the way you want. I am going to be dyeing my hair half and half now. I was going to take a couple of different shades of purple blue and green and then just like pick bits of my hair and dye it but I thought yes that’s cool but I’m gonna do split hair..