When you first install Windows 8, you are given the opportunity to choose the color scheme and background of the Start screen. Many users think that this choice is their one opportunity to control their background color scheme, but it's actually not the case. This tutorial will teach you how to change the background of your Windows 8 computer after its initial installation.
Personalize the Color and Background of Start Screen
Open the Charms bar and go to Settings > Personalize:
Once you have selected your new background for the Start screen, you can define the background and accent color: