Whenever something like this comes up, I have a standard reply that looks like this: “Ok, sure, neither of us can define a ‘salad,’ but would you agree that we can can define an ordinal scale of ‘saladness’ and mostly agree on the relative orderings of different things along it? Good, then I think we’re done here, all that’s left is the social convention about where along that axis we stop using the word.”
Also, I recently had (a self-aware and joking version of) this exact conversation where someone said ‘purple’ isn’t real. Again, simple answer: From a physics perspective, obviously there are no ‘real’ color categories. From a psychological perspective, obviously we use a three-axis color representation, where ‘purple’ is as well-defined as any other combination. The answer is entirely about why you’re asking the question.
I know this can all be adequately explained by perfectly normal human motivations, but there’s still a small part of me that wonders if some of the unfortunate changes are being influenced by some of the very factors (persuasion, deception, sandbagging, etc.) that are potentially so worrying.