I dyed my hair black and i need help getting a blue tint.?

I have naturally black hair but what I used to do to my cousin who is a blondie is mix a black and blue dye and then apply to her hair. It would look pure black then within 2 or 3 days you would see that awesome blue tint in her black hair. What you can do after the black rinses off ( I say after because dyes damage hair) is combine the midnight black and the blue -- depending how much blue you mix in will depend on how tinted the blue will look. I usually add half or a little less than half to add a solid black with a blue tint. My cousin always gets the your hair is soo black It looks dark blue.