On WOOL and other protein fibers, with our neutral pH water, Koolaid sets permanently without vinegar. The citric acid already in it is enough to make the dye bath the right pH for mild acid dyes. The color exhausts completely and the first rinse is clear. It's wash fast (even resisted bleaching in one test) and only the grape seems to poorly light fast.
On COTTON, however, it did not exhaust & the color faded in the first rinses, finally going to a very weak pastel stain after just a couple of washings. That has been my experience with the stuff.
In other words, it behaved just as you'd expect any acid dye to behave. Though it works out to cost a lot more than buying concentrated dyes like Jacquard, if you're just doing a few skeins, it's convenient and fun. The citric acid also helps the particle size stay much larger than most dye powders, reducing that inhalation hazard.
Helen "Halla" Fleischer, Fantasy & Fiber Artist