This blue drink turns purple then red/pink upon addition of a citric acid-boosted can of Sprite. It tastes good and has a similar chemical profile to a hypotonic sports drink (also see this homemade sports drink recipe).
It's the kid-friendly version of the Color-Changing Martini
- and it's much cheaper and more convenient than buying martini ingredients and dry ice. It's basically a classic chemistry demonstration you can drink. Note: I published this instructable in 2010, but unpublished it while I developed it further as a submission to the American Chemical Society's
Journal of Chemical Education. The article has now appeared, so for those of you who happen to have electronic access to this journal (probably because you are connected through a university network), you can find the manuscript online here.