A Kool-Aid hair dye job will last anywhere from a couple washings to four weeks.
More Info: Most Kool-Aid dye jobs will fade out within a few washings, especially if the hair is dark or the dye job is weak. If proper steps are taken, or if the hair is lighter, the dye job may last for many weeks. How long the dye job will last depends on the state of the hair and the method of dying. If the hair is dry or damaged, or the Kool-Aid mix is hot, the color will be more vibrant and last longer. If the hair is conditioned or greasy, and the Kool-Aid is a cold temperature, the color will last for a shorter time. In addition, the longer the dye is left in, the more permanent the color - some people leave the Kool-Aid dye in for a few minutes, others all night.
Kool-Aid is not actually intended to be a hair dye, but is often used as a short-term solution for costumes. It is also used to get "unique" colors that are harder to find in stores, like bright blues and purples. The different Kool-Aid flavors can be mixed to create new shades; try out Orange and Tropical Punch for a bright red-orange, or Lime and Blue Raspberry for an electric blue-green. Just like any dye job, Kool-Aid can be used with different tools and effects to result in anything from a realistic auburn to a rainbow gradient. As a warning note, most users try to find sugarless Kool-Aid to prevent a sticky after effect. Even with sugarless Kool-Aid, the hair will take on the scent of the drink mix. This can attract bugs during the summer, so be careful!