Microsoft had released the developer preview of Windows 8, next generation OS. The Developer preview version had very less customization options as it was intended to be a preview version. With beta version slated for release on February 29th 2012, we might see more customization options. If you are running developer preview version, you can try out this nature theme for Windows 8. This theme is extracted from the beta build and can be used on developer preview version as well.
The theme features 4 HD and 2 widescreen wallpapers and also allows you to set Windows aero color as automatic, this means it changes based on the wallpaper color.
Please note the extension of theme is .deskthemepack and this is not compatible with Windows 7. Alternatively you can use WinRAR to extract the images from the theme.