sure, a wavelength of around 532nm coming into your eye causes it to happen, but thats just information. Then its processed in your brain and at some point recognized as green. Somewhere in this, you see green, but you seeing it cannot be measured. Maybe the activations of your neurons could be, and maybe that could even be fully reverse engineered to understand how the conclusion of seeing green is reached. And yet, the actual stuff in your conscious experience still isn't there, just a bunch of logic is.
Now maybe we could discover some dynamics of consciousness though. If we create conscious AI or some way to inject new logic into our brain that is directly witnessed, we could probe for what configurations produce what kind of consciousness. So at least we could understand the behavior of it. But the actual stuff of it is not measurable by anything but itself.
I suspect that one is more likely to understand "green" by realizing that it is a word (originally, a sound) that you have come to associate with memories of visual experiences. To say something is green is to do a comparison between an aspect of the experience of it, and aspects of some of those memories of prior experiences.
I use color as an example because its very distant and theoretically could be many different ways (e.g. your experience of green may not be made of the same stuff my green is). However geometry seems far less arbitrary. Visualizing a square is more specific, the way the lines relate to space in the 2D plane if misrepresented will be wrong. I doubt we visualize such things with 100% accuracy, but we must visualize them to a certain common accuracy, and thats important, common. Basically, as far as experiencing the visual concept of a square, we all experience roughly the same object in our conscious experience. Thats where things can be studied a bit, because the behavior of consciousness given certain logic is likely absolute.
Yes, words are symbols. But when we're talking about consciousness, we're talking about the experience itself, not the association between the word and the experience. And we have no understanding of why or how the experience exists in us.
As for having an opinion, on the other hand, that usually depends on which remarkable circumstance one thinks is less implausible.
It can express this measurement in a representational form however, so we can study consciousness's behavior or the behavior of qualia.
-- David Foster Wallace
-- Albion ( https://i.imgur.com/8GHPl6S.png )
> Among the many forms of alienation, the most frequent one is alienation in language. If I express a feeling with a word, let us say, if I say "I love you," the word is meant to be an indication of the reality which exists within myself, the power of my loving. The word "love" is meant to be a symbol of the fact love, but as soon as it is spoken it tends to assume a life of its own, it becomes a reality. I am under the illusion that the saying of the word is the equivalent of the experience, and soon I say the word and feel nothing, except the thought of love which the word expresses. The alienation of language shows the whole complexity of alienation. Language is one of the most precious human achievements; to avoid alienation by not speaking would be foolish -- yet one must be always aware of the danger of the spoken word, that it threatens to substitute itself for the living experience.
-- Erich Fromm ( https://www.marxists.org/archive/fromm/works/1961/man/ )
For how a color looks to you, or just for the wavelength of light something emits?
1. Someone figures out in a lab all possible causes of fear via the surveying method. Fear seems solved.
2. New people appear that claim to experience fear when someone taps their left feet.
3. You have to redo 1. Therefore fear wasn't solved in the first place.
Replace "tapping left feet" with something more obscure, or fear with pain, to continue.
Underlying problem: you cannot compute the "preimage" of fear.