Microsoft teased a new Windows 10 Start Menu that features partially transparent theme-aware tiles to showcase the new Fluent-based colorful icons. Windows 10 version 20H2, which is now rolling out to seekers, uses the tiles with a colored background. Microsoft is planning to bring the same tiles experience to the splash screens of UWP apps, such as Microsoft Store and Settings. The next update will fresh up the Start Menu to remove solid color backplates behind the logos in the apps list and create a beautiful uniform design.
Source: https://www.bleepingcomputer.com/news/microsoft/a-closer-look-at-windows-10s-brand-new-start-menu/