Hi all... I have a lady who is 100% white and I've been using kp 99/0 6% on her roots and just a few darker one put through to break it up. Well the problem is she has been saying the 99/0 is too dark and a bit yellow looking lately so said she wanted a 10 which I explained would do nothing but she insisted anyway just to see what it would look like. Well 3 weeks later texts to say I was right it hasn't covered. I'm stumped really as you can't go any lighter than a 9 or it won't cover 😳