Upgrading the app «Google Contacts» 3.2 for Android appeared dark theme. You must enable it manually in the sidebar of the program.
To activate the dark theme need to stop the app via system settings. To download the updated «Contacts» in the Play Store or APKMirror.
At the event, Android Dev Summit company told about the results of the study of the influence of the dark elements of the interface to the battery of the smartphone. It turned out that the dark theme is several times more economical than light.
Now Google releases a few Android apps with an optional dark theme: «news», «Messages» and YouTube.