When you decide to let your grey hair grow out, the only real approach is cutting the length to help speed the dark ends in meeting the silver that's sprouting from your scalp! I'm going in for a bob on Weds., with slight layering at the ends...and some more lowlights to lessen the skunkiness of it all! Not an easy process... Supposedly it takes about a year to fully grow out. It can't come soon enough.
Below this pic is the silver-haired goddess, Sarah Harris. So stylish...of course with her long legs and lithe frame, green hair would look good! This article talks all about her decision to stay grey: http://intothegloss.com/2014/06/sarah-harris-vogue-uk/