You are doing an admirable job of recreating the course of philosophical development. I wish I could call it "progress", but this is, I believe, an iconic example which illustrates it is not. Thousands of years before humans discovered the real nature of colors (both as frequencies of electromagnetic radiation differentially effecting the cells in our eyeballs, and as comparative/relative signals processed by our neurological visual systems) Aristotle and other ancient philosophers contemplated the idea or ideal of the conscious experience of color (what today philosophers identify as qualia). But the question of whether "redness" exists 'in and of itself' is more a matter of convention than ascertainable fact. I believe (I'm not rigorously academic so I could be mistaken, and I'm sure I'm not using the "proper" terminology) that the current convention is to say that redness is always applied to something, similar to the idea of size; it is comparative rather than fundamental.

The truth, at least as I see it, is that this epistemic uncertainty is the same in terms of qualia like "redness" and also numbers, but also every other word in every real language. It just becomes most obvious in these two examples, so much so that not even the most neopostmodern of postmodernists can deny that metaphysical uncertainty (whether "red" exists or whether "math" transcends physics or results from it) and epistemic uncertainty (whether "redness" exists or whether "numbers are real") themselves exist (distinct from simple ignorance), and will argue whether they can really be distinguished.