Regardless of the actual merit of the alkali theory, the color shifts of anthocyanins (like those found in grapes and berries) when they change PH is striking. They turn from these almost bloody hues into brilliant azures.
If you like this kind of stuff then you might like Ink gin which changes colour when you add tonic. (https://www.inkgin.com/ - no commercial connection here, I've just enjoyed some of their products. :)
