Google dark themes have been grayer than the pitch/AMOLED black preferred by some. Google is now testing a completely black dark theme for Search on desktop web. Instead of dark grey, the background of Search result pages switches to #000000. Other colors for links and previously visited pages are similarly tweaked to be slightly bolder and less muted.
If Google Search decides to use black, the company will hopefully retain the old dark theme as a user-selectable option.This change has been appearing for some, but not all, users in recent days. The first people to receive the theme have already lost it. The rollout does not appear to be specific to any operating system.