I'm not sure how to break that phrase down further. Section 3 of that SEP article covers the issue, but the writing is as awful as most of the SEP. It's a word for the redness of red as a phenomenon of the nervous system, which is broadly similar between humans (since complex adaptations have to be universal to evolve).

But all this is an attempt to rescue the word "qualia". Again, I suggest expanding the word to whatever it is we're actually talking about in terms of the problem it's being raised as an issue concerning.