Google has released an update for mobile apps Contacts, which brought the dark theme.
Recently Google confirmed that, and so many knew the dark theme really helps to save battery on phones with OLED screens. And after just a couple of days ago the company released an update for Contacts app, which now also include the Dark Theme.
To activate the dark theme by clicking on the appropriate item in the sidebar
Dark color theme available in Google Contacts version 3.2.4. You can download it in Google Play or on APK Mirror. As for the next Google, which gets a dark subject, they should be the Google Phone.