I'll try my best to give you my answer. But I maintain that this is still somewhat subjective.
Firstly, I think the short answer to your question as stated:
Do we know the physical-nature of “consciousness”?
I would personally say that our notion of 'sense' - that is, our ability to perceive stimuli, is not the same as consciousness (whatever "consciousness" means at this point). To me, and I think many others, the concept of 'consciousness' is simply being self-aware.
Science understands most if not all sensory pathways very well in terms of the electro-chemical and/or mechanical pathways involved.
To pick from your 4 options:
- Consciousness does not exist. It is just a myth.
- Consciousness exists, but it is nothing more than information and computation.
- Consciousness exists, but we do not know its nature.
- Consciousness exists, we know its nature, and that is more than information and computation.
I think we can rule out 1 - we know we have something that we call consciousness - else we wouldn't be having this conversation!
We can certainly rule out 4 as well because we also wouldn't be having this discussion if it's nature was understood by now! :)
My own opinion steers me toward 3. Though I think understanding it might actually be impossible.
To run with your example of perceiving the colour red, I concur that we understand the physical processes that have occurred to enable us to see, and understand that we saw, red.
However...this puts me in mind of a kind of brain-teaser people sometimes mention: how do I know that what I consider to be red, is the same thing you consider to be red. Now, I don't personally think there's much to this, as colour is a physical property, but it does raise the possibility that the 'concept of red' is not immutable between individuals.
Some more food for thought is whether we actually possess a consciousness. By which I mean, it is an extant, natural phenomenon, like energy for instance, and you either have it or you don't. The alternative is similar to the debate about free will vs. the illusion of free will (I personally fall on the side of thinking the latter). That is to say, do we merely have the illusion of consciousness?
Taking the discussion from the comments about pain and expanding further; just because I feel pain, I do not believe equates to consciousness. How far down the evolutionary tree do you have to travel before you would decide a creature has no 'consciousness'. Sure, we probably agree dogs are conscious, but are they self-aware? Do they exist any further than to satisfy their biological needs? Even if we say yes... how much further do you need to go? Are sharks self-aware? Are hag-fish or nematodes self aware? And yet, we know that all these organisms are capable of sensing pain. So it's clear that simple sensing pain is not enough.
The last thing I recall reading about the basis of consciousness (and the closest thing I think we have to an answer as to what the physical basis of consciousness is) is that it is an emergent property of a complex system like our brain. The degree of 'inter-connectedness' in our brains is what makes us intelligent (not just size), and current thinking is that it's the density and number of networks inside the brain that is key.