Windows 8 has new Metro UI interface which is a new innovation by Microsoft, Some people liked it while others don’t like it. Microsoft has adapt this Metro UI from Windows Phone Operating System. It has default color setting in this interface and you are unable to change different colour settings for its Metro UI. Atleast it is not available in Developer Preview, may be it will available in Final build. But as of now, you do not have any option to change Metro UI color setting. Door 2 Windows has released a tool to change default color scheme for Windows 8.

This tool can change color for Start Screen and Logon Screen, Start Screen Tiles, Start Screen Tiles Fonts, Charm Sidebar, Charm Sidebar Item Hover, Network Charm Item Hover and Charm Sidebar Item Selected. After opening this application, You will see the default scheme and just click on any color you want to change it will open color picker, just choose color of your choice and customize the color in Metro UI and if you want default setting again, you can restore it anytime using the same application by clicking on “Restore All”. Make sure you launch the application with admin privilege or run as administrator.
Download and Source 1
Source 2