It looks like Google is in the process of rolling out a new update for the
YouTube app, which will add a new dark mode, similar to the one that's been released on desktop last year.
Nothing else seems to have been implemented except for this new dark theme, but one thing that's worth mentioning is the update will only be available to iOS users initially.
The folks over at
The Verge report Google plans to introduce the dark mode to the
Android version of YouTube “soon.” In case you're wondering why a Google service is getting a new feature on iOS before Android, we can't really tell why is that happening in this case, but it's probably related to the fact that YouTube has two different teams handling development for the two platforms.
It remains to be seen when exactly
YouTube for Android will get the new feature, though we kind of expect it “to go dark” in the next couple of weeks.