I colored someone's hair today, she had white /grey regrowth and a level 9 on the rest. I tried to get her to an even level 6, applied to roots first, used 20vol all over and mixed equal parts, left on for 35min under heat, most of it came out good except the roots (white) hardly took. Was I supposed to apply a violet base on the roots only and then my level 6? I've been out of the salon for 5yrs now, was only in for 2 after school, I'm forgetting my basics, help!!