Windows 8 Sapphire
Welcome to Windows Sapphire. This is your Start Screen. It's used to access your files, apps, and widgets. Think of it as your "Dashboard". In your settings, you have the option of booting to "Start Screen" or "Desktop".
* Custom Start Screen Backgrounds
* Custom Tint Colors
* Start Screen Transparency Options
* Use "Desktop Background" Option
Windows 8 Start Screen backgrounds are limited. Tiles cover up most of the screen and block off what's seen in the background. So in this case, what's the point of having "locked-down" wallpapers focused on design elements on the top and bottom? Giving the user ability to shift tints of color overlays is the best option.
Some users won't have a lot of tiles on their screen and would prefer a wallpaper in full blown-out color, or maybe even something fun and creative that "plays with the way the tiles are seen". Some users like to have their Desktop and Start Screen with a cohesive look and feel, but maybe with a little tint change.
This is the "start" of a fun Desktop and Modern UI user-experience, on update Windows 8.