According to a Reddit poster, Google is currently testing a Dark Mode for the Google feed. The latter consists of cards containing personalized news, sports and other information found to the left of the home screen on Android devices. This is an A/B test for Android 9 Pie, which means that those with a Google Pixel handset and the Essential Phone could receive the option.
Dark Mode changes how a page looks on your phone's display. Instead of showing a white background with black text, Dark Mode reverses this to a black background with white text. With this feature enabled in the dark, your eyes won't be negatively impacted by the bright white background, which actually can cause them to feel discomfort. The "pill" at the top of the Google feed that shows your local weather will continue to be shown with dark text and a white background.
Starting with Android 8.0 Oreo, Google rolled out a Dark Mode for the Pixel Launcher, Quick Settings, app list and the Google feed that would appear depending on the wallpaper you selected for your handset. This wasn't truly a Dark Mode for the Google feed since it still appeared with the traditional black text on a white background. However, the spaces between boxes were made to look darker. What Google is testing on the latest build of Android does carry the black background with white text as you can see from the image that accompanies this article.
Google continues to add Dark Mode to several apps. Recently, both Android Messages and the YouTube app for Android were updated to include the retina-saving feature.