I’ve played a few IFComp games this year that use both light mode (dark text on light background) and dark mode (light text on dark background) on different pages, and every time I’ve found it very jarring. I’m a dark mode preferer, so when I play a light mode game I turn my monitor’s brightness way down—but if a game suddenly switches to dark mode in the middle, I then have to bump up the brightness. Then just when I’m settling into reading the comfortable dark mode text, oh no, it changes to light mode again, blinding me momentarily until I get the brightness turned back down.
So my request/advice to authors is, avoid doing this, and rely on other methods to change the ambiance instead! (I’ll point to Pharos Fidelis from IFComp as a great example—the player can choose between light mode and dark mode, and the appearance changes that take place as you play are all in the background, not affecting the text itself at all.)