In several screenshots leaked online, we get to know that the Google News is next in the list to get the Dark Mode. It seems Google is now switching to Dark mode gradually, so as to use the OLED panel on their device into a good use. The Dark theme, not so dark, can save battery usage up to an extent.
The app update is rolling out gradually. Not everyone is getting the app update for now.
You can see this Twitter post which showcases the dark mode.
— David Slawotsky (@D_Slawotsky) October 5, 2018
You might even get the option to use the dark mode for a permanent basis as well. As usual, you can also schedule the dark mode as well.
Source: Android Authority