My hair originally was platnium blonde, over time I've added toner etc to get it darker & darker blonde. Over time my blonde turns yellowish.. my roots show & anyway my heads in a few diff colors & @ this point I usually go spend bookoos of money to professionally get it bk looking good.. but I'm tired of blowing money. I want to do it at home. I'm a natural blonde but older I get the darker my roots get. I bought warm light brown at sallys. Ion brand. Loved the color... would def go darker though. Its washing out more & more as its suppose to but now my heads more blonde again... w/ alil brown.. looks odd. How long do I have to wait to apply demi permanente color to get it bk brown? My hairs taking a beating from keeping it platnium. Blonde, so I want to be as gentle as possible.