First, let me just say that it's very difficult to get hair to be perfectly white. Depending on your hair color, you may need to bleach your hair a couple of times before it turns to white.
1. Bleach your hair with Manic Panic, dry, determine hair color, if it's not very light blonde, you need to bleach it again, it's best to wait a week before bleaching it again, but if you can't wait and doesn't mind damaged hair, you can continue. Bleach no more than three times.
2. Get a blue or violet based toner to take out any yellow color.
3. You will need to use a purple shampoo or tone regularly to keep your hair white, otherwise it will turn yellow or brass.
4. Remember to deep condition your hair regularly after bleaching.