The October update for Windows 10 is currently being rolled out to the general public. For those in the Fast ring of the Insider Preview program, however, the build of the future is available to try out. This update, known as 19H1, includes an improved Light Theme and some other things Microsoft had promised.
https://www.notebookcheck.net/Microsoft-releases-new-Windows-10-19H1-build-to-Insider-Preview.361756.0.html