I used this on very light white/ silver hair. I just wanted some cute pastel strokes. I left it in for an hour and blow dried it with a bag around my hair like the bottle says. But after washing it out there was no trace of green anywhere to find. Then I tried it again, repeated all the above but left it in for 2 hours this time. All I ended up with, was an almost invisible green glow if you look very closely...... Very disappointed.