This is according to a toggle that was spotted that allowed users to choose between either toggling a dark or light mode. As it stands, Android supports a dark mode but this can’t be enabled manually. What happens is that Android will adapt its look according to the wallpaper that users have chosen.
So for example when users pick a dark wallpaper, the rest of Android will change to match the look accordingly. However like we said, this isn’t a manual process in which some users might actually prefer having more control. However with this feature, users have the option, but as Android Police notes, this is a feature that is part of the Pixel launcher.
This means that it is unclear if other non-Pixel Android smartphones will be able to take advantage of it, but we suppose that remains to be seen when Android P is finally rolled out to the masses, which should be later this year.