Sort of, but not the way you mention.
eReader devices and most software readers have that capability built-in. It's a good idea to test your rulebooks to make sure they work in both situations. Images including dark text on transparent backgrounds or light text on transparent backgrounds are the biggest culprits, as the background will change dynamically, but the image may not. I tend to put a stroke around text that needs to be in images like that.
For accessibility, PDFs are kind of terrible. ePubs or other non-fixed layout formats are better -- for the aforementioned day/night swap, but also being able to zoom the text without having the scroll all around the document with a virtual magnifying glass. If you also want to get real into it, try feeding your game into a screen reader. It's an experience.
That said, all this comes along with trade-offs in visual layout control (as a lot is now in the hands of the user). It's up to you as a designer if that cost is worth it. For me, it usually is.