His claim was that there was something that could only be learned about the color red...

That's the issue. I don't think you learn something about the color red; I think you learn something about your mind. There is no objective thing that red looks like; it is the result of certain neurons firing. If Mary's brain were wired differently, the experience of seeing red light would be different if it even existed. The only relevant thing about red light is that it stimulates certain neurons; if you knew absolutely nothing about it except that, you could fully describe explain Mary's experience of seeing red (in theory, of course; neuroscience ain't there yet). On the other hand, you couldn't explain the experience with unlimited information about red light plus only the fact that it stimulated Mary's retina.