Simple two-color pairs - potentially used in combination to create a whole palette. Liking combinations of vibrant & muted tones - keeping in mind legibility!
It is seeming as though the general thesis of this benchmarking is that I'm really interested in one-page websites with lots of drawers, which I think could work really well for this fairly concise, well organized content. Not all of these examples have comparable content, but I think they all propose a system that could accommodate an easily accessible table of contents and a modular space for chapter content.
The websites here are more for layout rather than visual reference, but I do generally find much of their simple, type-forward design helpful.