> So it's entirely possible that tetrachromats map their four rods to the same RYGB box the rest of us perceive as qualia, only with a different mapping.
If they did this then wouldn't they necessarily also confuse some colours that trichromats can distinguish?
I think certainly, yes. I wonder if that's been researched?
That wouldn't prove, but it would strongly suggest, that they're seeing the same qualia as the rest of us in the end, just mapped differently. Particularly if we could find "symmetries" -- i.e. for each area of new distinction they see, there's a corresponding area of distinction that collapses.
If they did this then wouldn't they necessarily also confuse some colours that trichromats can distinguish?