If the food is chemically identical then the taste would be the same though, since taste (and smell) is about chemistry. I do get what you're saying though.
An interesting thought experiment, but there's a flaw in it, an implicit fallacy that's probably a straw man. On its own, the argument would likely stand that Mary gains new knowledge on actually being exposed to color.
However, there is a broader context: this is supporting an argument against physicalism, and in this light it falls apart. There are a couple of missing bits required to complete the experiment in this context. The understanding that knowledge comes in 2 varieties: direct (actual experience) and indirect (description by one with the actual experience using shared language). This understanding brings proper clarity to the original argument, as we are aware - I think - that language is used to create compressed representations of things; something like a perceptual hash function.
The other key bit, which I guess we've only considered and extensively explored after the argument was formulated, is that all information coming in via the senses goes to the brain as electrical signals. And we actually have experimental data showing that sensory information can be emulated using machines. Thus, the original argument, to be relevant to the context, should be completed by giving Mary access to a machine that she can program to emulate the electrical signals that represent color experience.
I posit that without access to that hypothetical machine, given the context of the experiment, it cannot be said that Mary has "learned everything there is to learn about color". And once she has comprehensively and correctly utilized said machine on herself, she will gain no new knowledge when she is exposed to the world of color. Therefore this experiment cannot be used as an argument against physicalism as originally intended.
OK. I enjoyed the mental exercise though, thanks for that. Also, as someone who's formally studied philosophy, I'd say there is definitely value in thought experiments, particularly as I think we got to an objective level in this case, though we started with the subjective. And determining universal (objective) rules are valued as they usually help guide us to truth, and/or point to ideals to strive for.
This may come off as pedantic, but "identical" is a very strong term when it comes to something like chemistry. The smallest chemical difference can manifest as a large physical difference. Consider that genetically, humans are about 60% similar to the fruit fly, yet phenotically, the similarity could be considered under 1%.
