What made my garlic turn bright blue when I added it to a relish mix?

The mix was vinegar, cooked egg plant, tumeric, herbs and spices. The blue was a royal blue. It was very pretty but disconcerting.

What made my garlic turn bright blue when I added it to a relish mix?
The problem is with the salt,you have to use canning salt when using vinegar to preserve, regular salt won't kill you but use canning salt instead