https://www.bleepingcomputer.com/news/microsoft/a-closer-look-at-the-new-windows-10-light-theme/

The headline feature of Windows 10 May 2019 Update is probably the Windows Sandbox, but another useful addition is the new light theme for your Windows desktop.

Prior to May 2019 Update, Windows 10 had two color modes - light and dark. The light mode allows apps and programs to use white color, while the dark mode enabled the use of darker colors and accents.