Because when hair has been coloured to an artificial grey, the underlying base still needs to be pure white. Those who have created an artificial grey often complain about the shade turning a murky green after several washes. This occurs because the bleached/lightened base is yellow, whereas the grey shade is blue based. Therefore, when blue and yellow mix – green is produced. In order to continue displaying artificial grey, you must keep neutralising the underlying yellow tone. Therefore, whenever the grey hair begins to turn green, use Colour Restore Iced Platinum. The acid violet molecule will neutralise the underlying yellow tone back to white and the artificial grey will again display correctly.