The sense of “what is,” is a curious but fickle thing.
Qualia, as a term, is the sense of being, the redness of red, the smell of a rose, what it is like to feel pain. An experience, only describable by its nature, by its experience.
Describing the quality of color to someone who is completely blind, is a quale. We can ask many questions of a quale, but never describe it, to someone who cannot feel pain, it is undescribable to them what it is, which is the main essence of the idea of a qualia.
Qualia can bring into the question an example of how this affects how we know the colors we see, are the colors others see, our own subjective experience of color may be different, but there would be no way of testing this, as the color spectrum would match up the same, we would still see, the same, our conceived notion of color, and light, would be the same. Our preconceived notion of what is, may not be what is, what if we discovered a new color on the spectrum of possibilities, how would we describe it, why can we not create new colors, that no one has seen. Because we have no preconceived ideas and experiences of these things, it is impossible to describe. How do we try to explain green, we describe it by its, “Greenness” and what objects have the color.
In its most dulled down nature, qualia is the raw experience of something, the feeling of touch, the sense of pain, the taste of wine, the smell of a flower, the color of the sky; are these unique, raw, unexplainable experiences, only by experiencing that state of mind in which you are experiencing them.
“Experience is the teacher of all things.” – Julius Caesar