Those who are going crazy with the amount of white in Google's latest redesigns have probably calmed down thinking about the next dark modes. More recently, the Google app, Files by Google, Google Drive and Google Keep have received UIs dark and Gmail may be next. The latest APK in Gmail contains the first view in a dark mode, although it is sporadic and only in settings.
The screenshots above show what we're seeing in Gmail v2019.06.09. The dark mode does not currently have a toggle and it goes in and out whenever you want, but here's a first glance. It only appears in the settings, not in the main window or sidebar. We know it's not too far, but I hope this calms some of you who are waiting for the dark mood in one of Google's most-used apps.
If you just have to take a look at this dark Gmail mode for yourself, you can grab APK v2019.06.09 from Gmail in the Mirror APK. Again, there is not much to see beyond the pictures above, but do what you want.