I just noticed my OneNote for Android has dark mode enabled. I’d read from reports in April that this was coming, and that it would mirror the theme settings on the PC connected to the same account, but my PC OneNote is currently set to the Light theme.
The dark theme isn’t perfect though. It looks like it needs some work with the font colors. I’m on Android 7.1.1.
I didn’t do anything to activate it, so my guess is that it’s a server side activation or test. I would’ve posted more pictures, but then there’ll be privacy issues.
I’ll continue testing this & will provide updates, if anything changes.