Tyler blogs about qualia today here. Qualia are of course the subjective experiences that occur as part of our conscious selves when we see something like the color “red”. The argument is whether my subjective experience of red is the same as yours? This is an interesting question. It’s quite separate from the cognitive process of labeling things as “red”. It’s the experience of “redness”. As pointed out, my experience of “redness” might well correspond to your experience of “blueness”. It’s something inside our conscious selves that we can’t share. That in spite of natural selection and our visual color system (to say nothing of language) causing us to label red frequencies of light as “red”.
Experience is part of what David Chalmer’s calls the “hard problem” of explaining consciousness. You can read more about that here.