10-15 minutes and wash sounded like a very short time to keep a dye on your head, but I obeyed. My hair was stained all purple and I went "nooooo not again!". This has happened to me before, when I kept silver shampoo on my head for very long. I washed my hair with normal shampoo immediately and the purple color faded quite well. However, on wet hair, the impression was "dirty". It was light purple at the top of the head and light yellow at the roots - the comparison making the blonde parts look even a bit green. I dried my hair and the purpleness settled a bit. Okay, better. My hair looks white now, but it's normal blonde at the roots, making it look slightly goofy. I wasn't expecting the color to stick onto the roots though.. But still. When you want white or silver hair you just have to know what you're doing: It's the most difficult color to achieve and most of the time it's always too yellow or too purple. Take a risk?