This is a few washes post black.  I used to have 50/50 split dye and would keep the blonde and black separate but having these chunky highlights has been the bane of my existence. I used to clip them up when washing but gave up as it took so much time. 
I wash with as cold a water as i can but i have massive shower sensory problems so it’s not easy. 
One side of my hair fades so quick cuz it used to be near platinum. not a problem ig.
But since my hair is pretty damaged the dye literally falls out nd looks good for about a week.
My partner uses the same dye and it stays almost jet black until we have to retouch it and he uses the same shampoo and conditioner as me!
Anyway, 
I use Live deep black 099 dye.
Drugstore apple shampoo (alberto balsam) 
Garnier papaya hair food conditioner 
or
Maui revive and hydrate conditioner less often

My hair is also very greasy, so i wash it every 2nd dsy. also i wash it twice in the shower 

So i ‘try’ to keep harsh chemicals to a minimum. I used to use shea moisture leave in conditioner everyday along with their conditioner. but tbh i didn’t see any difference.

I just want my hair to be semi healthy again. AND KEEP ITS FKN COLOUR. i’ve not had bleach near it for about 4-6months. i’ve not had heat near it for almost 2 years. 

Washing black hair recommendations (PLZ HELP)