1) let hair get as dirty/go as long with washing as possible
2) brush hair with a soft bristly brush (like a boar hair type brush) from root to tip, drawing the natural oil through the whole hair shaft, the morning of
3) that night, when your hair is good and greasy and dirty, wash with dish-soap (try to get color/fragrance free)
4) make a paste with 1 c of baking powder and warm water until its a loose paste- rub and scrub thoroughly through hair, let sit 20-30 mins. Rinse.
5) wash with a moisturizing shampoo for heinously damaged hair, rise.
6). Towel dry hair, cover aggressively with deep leave-in conditioner, cover head with a showercap and let sit overnight.
7) deep condition overnight like that, and wash normally, for a week (or as long as you can). A leave in conditioner with protein is ideal.
8) at this point the most color possible will have been lifted/stripped from your hair, and it'll be moderately well moisturized/back into halfway functional shape before dying again.
I had platinum/white blonde hair for 10 years, and alternated between pink, blue, and lime green for 1-2 years before that. And this worked best for me.
i am so vain. and yet, so masochistic. how can the two coexist?