There's a yellow mica pigment that when used in soap making it turns a very reddish-orange (almost like rust) until the saponification has completed and then returns to yellow. It is very disheartening the first time you see it and start to think how your batch of soap is going to not be what you hoped, and then 24 hours later it looks exactly how you hoped.
That would be my guess as well. After thinking about this further, I do remember as a kid using the kits for dying eggs for easter (somewhat belated topic) that required vinegar instead of water. The yellow dye would also appear orange until it dried as yellow. So, yeah, I'm leaning towards the pH as to the cause, but we still don't know the reason. I'm going to deliberately NOT go down that rabbit hole...*
"An acid-base indicator is an organic compound that changes color with a change in pH. Methyl orange is a very common acid-base indicator, red in solutions that have pH values less than 3.2 and yellow in solutions with pH greater than 4.4. Indicators change color because the chromophoric system is changed by an acid base reaction (see below)."
https://chem.libretexts.org/Ancillary_Materials/Laboratory_E...
* I swear I tried really hard. Luckily, the hole wasn't too deep
