Books don't emit light in the visible spectrum so it does not make it easier on the eyes in low light conditions.

Historically it's also cheaper because paper is some shade of white and it's cheaper to not soak the page in ink.

Black or coloured papers, and non-black ink, cost more than plain white-ish paper and black ink.

The Guardians of Childhood series has a few chapters that are printed in "dark mode."

In a physical medium, it's way cheaper and easier to make light color thing dark than make a dark colored thing light. "Dark mode" books would require dyeing each sheet black, then painting the text on top of each sheet, rather than what is currently done, where we bleach each sheet white, then dye the text into each sheet.

Somewhat related - this is why printers use CMYK, rather than RGB. Computer screens use pure light, so they simply emit whatever combination of light they need to, and your eyes add them together. In a physical medium, however, what we see is based on what is reflected, i.e. not absorbed. Hence, each color of ink, in additive terms, is two colors together (cyan is green+blue, magenta is red+blue, etc). When you combine CMYK colors, you can precisely control what wavelengths of light are being absorbed in order to reflect the correct color.

Hm. You can't print it like that, it'd a ton of ink and too heavy.

Black paper and white ink? That's interesting

There are dark mode books? Just not that many.

@GolfNovemberUniform Its bad for your eyes to read in the dark, some kids books do have black pages and white text, like horror ones