ok so a few days ago, i put some turmeric powder which was a bit old in water. then, i added eau de javel (which is a solution of NaClO and NaCl). the solution turned red. after a while, it became yellow again. could it be some kind of acid-base reaction? because that's what happens when we titrate acid/base solutions: the color of the indicator becomes transparent but then returns to its original color until we reach equivalence. could this be the same?

It's probably something similar. The bleach is alkaline and alkalis turn turmeric reddish. The change to yellow could be because it picks up CO2 from the air abd becomes less alkaline or it could be some more complicated reaction with the hypochlorite.

cool