Hello! I have a problem with Loreal Professional Majirel. It doesn't cover my grey roots, roots stay semi transparent and yellowish. I would highly appreciate if you tell me what I do wrong . I mix Majirel 7.0 (13 gr),6.0 (13 gr), 6.3 (6 gr) and 7.23 (6 gr) with 57 ml of 6% developer.