I always over ash , you want to know why? Different cities have different water. Every water has its own ph levels and minerals according to where it comes from . With every wash minerals exfoliate toners and color off your hair. Within 3-4 washes the toner wears down and the color becomes brighter and softer with less yellow. It's to benefit the client so they can enjoy a beautiful color longer and less on their pocket 😉 but hey 🤷♀️ what do I know I just do hair .