What chemical changes were responsible for the color changes? (while doing a red cabbage juice lab and finding out if substances were acid, base, or neutral based on what color they turned)

Hello!

The chemical changes that were responsible for the color changes while doing a red cabbage juice lab and finding out if the substances were acid, base, or neutral based on what color they turned, were the ph changes in the medium, which changed the structure of anthocyanins in the red cabbage juice. 

Red cabbage juice is composed of anthocyanins, chemical compounds which can form glycosidic bonds with sugars depending on the pH. If the pH changes, the glycosidic bonds will change too, affecting the molecule and changing the color we perceive. 

Have a nice day!