There is a product line called Trionics. They manufacture developers. Their grey be gone developer is equivalent to a 17% peroxide and you process under heat for 15 minutes. Find a salon that uses it, or find an open minded stylist who would purchase it especially for you. I guarantee it to cover the most resistant grey or pure white hair. It's an excellent product
I didn't have time to read through all 70 of the replies to this thread. Please accept my apoligies if you've already found a soloution to your problem.