I think it's arguable that this "conscious experience of nothing but constant redness" might not be actually possible. We can imagine it, of course, but we can

I think it's arguable that this "conscious experience of nothing but constant redness" might not be actually possible. We can imagine it, of course, but we can also imagine many things that can't actually exist in the world. It's similar to the idea about p-zombies: just because a concept exists doesn't mean it's physically realizable. It's very much possible that what we would call consciousness can only exist in certain types of minds that have a particular level of intelligence, but also a particular structure. Of course, it's also possible that you're right and the two are entirely separate, and that consciousness doesn't require intelligence (and possibly vice-versa).