Google is currently optimizing some of its core apps in order to comply with Android Q's system-wide dark mode. The latest of these spotted with such an update is Keep, a handy source of memos. Its new theme, while not available to all users, may appeal with its ease on the eyes and new custom colors.
https://www.notebookcheck.net/Google-Keep-will-be-upgraded-to-Dark-Mode-soon.421360.0.html