Ink, paper, and the colour between them
A palette is two decisions: what the ink is, and what it sits on. Everything else is adjustment.
Printers did not have palettes. They had an ink and a stock, and everything they could do with colour lived in the relationship between those two.
That constraint produced better-looking pages than most colour pickers do, because it forced the only two decisions that matter to be made first and deliberately.
Paper is a colour
Uncoated paper is not white. It is warm, faintly yellow, and it absorbs ink so the same black reads softer than it does on a coated sheet. Choosing the stock sets the highlight of everything printed on it, which means it sets the contrast of the whole book before a single word is placed.
Ink is rarely black
Trade books are commonly printed in a black that has been warmed slightly, because a neutral black on a warm sheet looks like a hole. The adjustment is small enough that no reader would name it and large enough that every reader feels it.
Translating the idea to a screen
A screen palette that begins from "what is the paper, what is the ink" produces calmer pages than one that begins from a brand colour. Set the background and the text colour first, and let the accent be the third decision rather than the first.
That is also the reason a good reading theme has so few colours in it. There were only ever two.