Someone suggested that the difference of vinegar or no vinegar with Kool-Aid dyeing could be that without vinegar may fade more over time than that dyed with vinegar. Okay... could be... so how to check this without waiting years and years to see. I decided to put it through a test that would be far more harsh than normal time, and to include Acid dyed wool in my experiment too.
I used samples of 3 colors of wool dyed with Kool-Aid alone, 3 colors dyed with Kool-Aid & vinegar, and 5 colors dyed with acid dyes. These were all put side by side on the dash of my truck for 21 very hot, sunny days. Yes, from 29 July to 18 August, the sun beat down on these samples, it's bleaching power amplified as it passed through the glass of the windshield.
All samples did fade to some degree. Acid Dyes definately stood up to this kind of abuse better than wools dyed with Kool-Aid, with or without vinegar, but the Kool-Aid with vinegar did seem to have a very slight advantage over just the drink mix by itself. So, if you plan to abuse your wollen items like this, I would advise using Acid Dyes, but if not, Kool-Aid without vinegar would likely be just fine, but remember, don't add sugar to the mix.