I bought some Pedialyte freezer pops for my kids:
And I've noticed that after spending a long enough time in the freezer, the purple "grape" pops change color from purple to green:
After thawing (but before melting), the color changes back from green to purple. The dramatic color change happens to all the purple freezer pops, and only the purple freezer pops. They taste the same afterwards and are safe to eat.
I couldn't find any decent explanations for this effect searching Google. This Reddit thread is about the same effect happening to purple Powerade:
There are hundreds of comments, but they are mostly jokes. The only thing I learned was that it was not related to Anthocyanin because purple Powerade does not contain that.
These are the ingredients of the freezer pops:
Except for perhaps "artificial and natural flavors", the only difference between the different types of freezer pops are the coloring: "grape" has Red 40 and Blue 1. The others are different combinations of Blue 1, Red 40, and Yellow 6.
I initially had a naive hypothesis that maybe Red 40 turns yellow when freezing (since blue + yellow = green). But the Orange and Cherry pops also have this ingredient and don't change color.
Some answers on the Reddit thread suggested that the color change is due to the combination of electrolytes and blue coloring, which is plausible given that Pedialyte has a lot of electrolytes. But "Blue Raspberry" also has Blue 1 and doesn't change color after freezing.
So, my question is:
What specifically causes the purple freezer pops to change color, and why doesn't it happen to the other flavors of freezer pops?