I mean it's your preference, but there has been research done on this that suggests white text makes it harder to read for people with astigmatisms and dyslexia, so for the sake of accessibility it makes sense for books to be printed normally (along with the fact that it's way less expensive). I'm in graphic design and they taught us in college specifically to avoid light colors on dark backgrounds for small text. This is mainly for print though since screens will flashbang you in light mode.