I dyed some wool using Kool-Aid (an American soft drink). I followed the instructions in a book called Kids Knitting by Melanie Falick (we Melanies are a darned talented bunch aren't we?). I won't reproduce her directions because they're copyright. If you want to dye yarn with Kool Aid without buying the book there are several sets of instructions on the Internet, for example at Knitty.com. Kool-Aid is not an everyday item in the UK and I had to buy some from KoolaidUK.com. I wonder if you can dye yarn with Ribena?
It was quick, easy and fun, and very effective. I was amazed at the depth of the colours, especially the purple from the grape flavour and the red from the cherry flavour. One amazing part of the process is that the coloured drink turns colourless as all the colour is taken up by the yarn. That was fun to watch. It also means there is no long tedious rinsing out of excess dye at the end of the process. Just a quick rinse in clean water then hang it out to dry. And the dyed yarns smell fruity, although presumably that vanishes the first time you wash it. It makes knitting with it fun, though.
There are other projects in Kids Knitting that I want to try. Watch this space.