The spray is bad because it runs when you sweat. I use Special Effects for my non natural colors and Nutrisse by Garnier for my natural color needs. My blue hair stayed blueish for about 1 and a half months. It is now back to almost normal, with somewhat of a greenish tint.
Non natural colors, blue, purple, pink tend to stay a shorter period of time and not take to the hair as well. If you have dark hair, you will want to bleech if you intend to get a vibrant color.
And a word of warning, the hair dye is a dye, and can and most likey will stain towels, skin, sinks. So far I have turned one hotel shower blue. The red that I dyed my hair last year at nats wasn't as strong and was a natural red color, and didn't stain the sink or shower.
And beware of getting the dye on you cheek...
