I´ve used the medium brown and light brown from B2N and my system became very dark. I only leave in shortly - 5 min. I would not recommended it as it ruined a system going very dark - almost blueish. I have not tried Aufero. Always make a colorsample on your own hair and the system. It may be time consuming but nothing against having to bleach it all out again

Best

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"They restore colour and they neutralise brassy tones"

B2B colors your system darker with shades of black