Now, that’s an important remark. Leaving aside the fact that speaking of “materialist” and “natural” explanations begs the question in the thread of whether those terms mean anything, and if they do how they arise; leaving that aside, I say, the wavelengths reaching the eye at sunset are not the aesthetic or spiritual experience - or even simply the visual one. Still less do they explain them.
Everything that creates what Ashwin eulogises - and everything that makes it possible for even someone unmoved by the experience to get what he is talking about - is downstream of that, in the mind.
The viewer sees no wavelengths - only red and orange and blue, which on materialism are mere epiphenomena. In fact, not only shifting colours, but an entire idea is constructed from the sensory data, memory complexes and cognition. That experience, on materialism, is entirely an epiphenomenon.
The colours, the shapes, the sound of the waves, the chill of the breeze, the smell of the sea - none of those exist outside the conscious mind, being interpretations of - who knows what, for all our investigations terminate in the sensory experiences of our minds.
Our minds are, by the very fact of their unified subjectivity (ie the indivisible “me”) are not explicable in terms of materials. They can only be experienced, or rather, they can only be the subject of experience. Nobody can, even in principle, make any number of “its” into an “I.”
Show the sunsest viewer a palette of the same colours, and it’s leave him cold. Show him a list of wavelengths and he’ll yawn.
So there’s a kind of choice to be made (though not necessarily an absolute dichotomy): either the mental world is an epiphenomenon on a real “material” world; reality being wavelengths, mass, velocity, and so on - a host of abstract and ultimately unknowable postulates.
Or else the real world is that of the mind, consisting of meaningful colours, smells, sounds - and indivisibly from them the spiritual impressions accompanying those experiences. Incidentally, it’s that mental world that also contains visual representations, through maths or writing, of the wavelengths, masses and the other 2nd-order things that the mind speculates as lying outside itself.
Now, it could be that real minds get their input from some “substrate” out there, which for want of a better word you can call “matter” (though “another mind” would be an equally valid explanation). But it’s pretty hard to see how it relates to reality. After all, if light is simply wavelengths, what exactly is it that makes my writing “500nm” less real than the blue you see out of the window on a sunny day?
It would seem that the answer is that your mind doesn’t experience a wavelength, “500nm,” as reality, whereas it does experience blue skies as reality - and here’s another conundrum: as you read this your mind can experience a blue sky from memory as a kind of reality, even if (like here) the sky is grey.