My mum has had Wella 6/77 on her hair for the last 10 years she’s 70 now and I feel it’s a bit dark for her so I’m planning to use a bleach bath to drop her one shade. I feel I’m over thinking the colour part but I need some help she’s 90% grey at her roots ( 1 inch regrowth and I’m presuming after I’ve lightened her hair it will be a very warm level 7 so I’m thinking of mixing equal parts of 77/0 with 7/7, can I put this on root to tip or will I get banding ?