I’m not sure how to answer this without being confusing. Methylene blue is not a pH indicator in the same sense that, say, phenolpthalein is with its characteristic color change between pH 8-9. Methylene blue does have a color change, but rather than being strictly pH-dependent, it is a function of the redox status of its environment. If it is under a net reducing environment, it will be a colorless, reduced compound. Under a net oxidizing environment it will be a blue, oxidized compound. That’s not to say that the redox environment can’t be linked to the pH in some way, but it’s the redox status that counts moreso than the pH, per se.
didn’t you do premilinary work in class
we had to do tests to see how much meth blue to use because it is in too high a concentration, what temperature range to use so we can get a good graph etc. Hope that helped