I have some acid dyes in my stash, but have not dyed yarn at home (did it once under the supervision of a yarn dyer at the Knitter's Guild meeting last September). My only concern is that the dyes are slightly toxic so I don't want to do it anywhere the cats hang out. Then I thought I'd check out the dyeing with Kool-Aid thing, since that's something you actually eat, you can use your kitchen and regular utencils to dye with.
We had grape and cherry in the house, so I used 2 parts grape to 1 part cherry wanting a fushcia type color. It was a very cool process, the water became clear once the yarn soaked up the dye and I do think the color came out pretty close to what I wanted - I was thinking of the lilac we have out back.