It would depend on what the liquid is, it might taste good. Most likely though it is for the "coolness" effect of being part of the "in" crowd.

However, I am trying to figure out what is causing the changes. It reminds me of using titration using methylene blue (I think) to determine PH. Chem lab was nearly 50 years ago and I haven't done that kind of stuff since then. If the PH of the drink is very close to the indicator change point it wouldn't take much change to make it turn blue. The escaping CO2 bubbles may be responsible for this (if that is the gas we see in the bubbles). But the confusing part for me is how it changes back and forth without any visible additions or changes to the solution.