This can vary depending on the brand but the manufacturers say:
This is only a rough guide and as frequent dyers will know some shades may only last a few washes whereas other may be hard to get rid of once on the hair. Always try a strand test and/or read product reviews to see the length of time the dye may last.
For more specific information please post in the main forum
cool, thanks! i have crazy colors one! (my bf brought from england, because i live in a backwards country, where no one has seen a person with blue hair - ever)
And remember that blues fade fast but pink stays forever. Also your hair is as individual as you are so what may last a few weeks on one person may last a longer or shorter time on you.
Manic Panic lasts quite a long time, but it does fade quite a bit. Crazy Colour probably goes the quickest though.
how long do you think manic panic amp purple haze would last?
That would depend on your hair type, hair condition, if you have colour build up etc. Also the amount of times you wash your hair can make a difference.