"Fantasy" or wild hair color that actually works.
First of all, let me explain how "crazy" or "wild" hair color works.
Bold colors like blue, purple, pink, candy apple red, yellow, green, etc usually only come in the form of semi permanent or demi permanent. These colors act as a stain to the hair and you get better results of the hair is pre-lightened (bleached) prior to applying. Since a semi/demi permanent color contains no ammonia, the hair cuticle isn't actually penetrated and so the color molecules don't actually get all into the hair shaft like a permanent color would. Instead, the color molecules just attach themselves to the hair surface (which is why fantasy colors fade so easily).
Now that you know how that works, let me actually get into the brands that have worked the best for me.
Pravana Vivids is my favorite brand of fantasy hair color. The only down side to this color is that it is only available to licensed professionals (or beauty school students). But if you can get your hands on Pravana, I swear you will never want to use anything else ever again. ALSO, the number one thing that I love about this color is that it is infused with silk and keratin protein so it leaves your hair all smooth and shiny :D (will last about 8 weeks before it starts to fade out)
RAW Hair Dye is my second favorite brand of color. You can get this at Hottopic and it leaves you with super bright and vibrant colors. (will last about 6 weeks before it fades out)
Special Effects (sfx) You can also find this at hottopic and its not as great as RAW but it works. (will last about 6 weeks before it fades out)
Beyond the zone/N'rage Two different brands but you can find both at Sally's. These are pretty decent. will last about 4 weeks depending on how often you wash your hair (i wash mine every other day, sometimes every 2 days and I always use cool water)
Manic Panic just never ever worked for me. When I triedmanic Panic, I had to redo my hair every time I washed it to keep it vibrant. I hated it.