The new theme, once available, can be activated by tapping on your account icon, selecting settings, and choosing "dark theme" to turn it on. Dark theme will invert many of the colors of the YouTube AI, replacing the traditional white background with a black background.
YouTube introduced a hidden dark mode feature for the desktop starting last year, and since then, the feature has been one of the most requested for its mobile apps.
The dark theme for mobile devices has been in testing for the last few months and it has been previously available to a small number of YouTube users.
You may not see the new dark theme available as an option right away, but it should be rolling out to all iOS users over the course of the day. YouTube also says a dark mode is coming to Android in the near future.
YouTube is a free download for iPhone and iPad. [Direct Link]