My permanent black hair dye keeps washing out!!!?

I use the expensive store bought brands. I have dyed my hair many times and I let it grow out and before when I dyed it would not wash out and have used the same stuff. My hair is very long, I don閳ユ獩 know if that could be a cause to it. I am using shampoo and conditioner for color treated hair. I am going to get the pantine pro v kind that is for black hair dye. I do cover the roots when I dye it and because of fading I put it on the rest of my hair. I can wash my hair after 4 weeks and the dye will still wash out!!

HELP!!!!

My permanent black hair dye keeps washing out!!!?

I have the same problem with permanent hair color.

My permanent black hair dye keeps washing out!!!?

Then it definately is not permanent

My permanent black hair dye keeps washing out!!!?

Try leaving the solution in longer