That’s amazing, but of course we literally can’t imagine the colors they see, because our brains aren’t evolved to do so. (And how does that relate to the philosophical notion of “qualia” and the so-called “hard problem of consciousness”?)

As far as our own human color vision goes, I read a report somewhere (unfortunately, I can’t remember the source) that a person who was both color blind because of a retinal defect and synesthesic reported seeing what he called “fairy colors” when he heard specific sounds — colors he couldn’t normally see.