Red cabbage is pretty versatile as an indicator, going from
yellow red in low pH (20% acetic) to blue, green, and then yellow as alkaline pH increases - almost like an inside-out universal indicator. [Corrected - thanks Dd]
Another natural indicator is sunflower seed anthocyanin made by soaking and filtering sunflower seeds with water. That one still needs the pH/colour response documenting but playing around with it demonstrated some useful colour changes. The sunflower extract seems amenable to preserving with alcohol (EtOH/IPA) too.
Attached is a picture of the cabbage juice but it sets me wondering whether the yellow is the high pH or the low. I'd best do some systematic tests with proper notes, then I can throw in some results for beetroot too, which has a simpler colour profile (red/yellow) more akin to phenolphthalein.
It's probably best to avoid phenolphthalein itself if you're intending to consume a product since it's a powerful laxative.
downwardsfromzero attached the following image(s):
20231018_162614.jpg
(2,089kb) downloaded 42 time(s). “There is a way of manipulating matter and energy so as to produce what modern scientists call 'a field of force'. The field acts on the observer and puts him in a privileged position vis-à-vis the universe. From this position he has access to the realities which are ordinarily hidden from us by time and space, matter and energy. This is what we call the Great Work."
― Jacques Bergier, quoting Fulcanelli