Hi geeks I have a lady who is 100% grey who wants just some slices of purple and silver (10 sp and 10 dl) I’m not going to do the 10’s I’m going to take it to the 8’s as she is a very salt and peppery grey. They do this in a permanent so if I add a ni shade in with my target shade will it cover?? I’ve nevet used them on 100% grey hair before. Thanks