Tutorial: How to get started with customizing the Metro Start Screen | Panda X
1. Download a hex editor. I chose HxD (http://mh-nexus.de/en/hxd/)
2. Navigate to C:\Windows\System32\
3. In the Ribbon click File > Open Command Prompt > Open Command Promt as Administrator
4. Type the following in CMD;
takeown /f uxtheme.dll
icacls uxtheme.dll /grant Administrators:F
5. Copy uxtheme.dll to the deskop.
6. Open your hex editor and open uxtheme.dll
7. Go to the hex location as shown in ‘Metro Customization – Hex Table.txt’ by hitting Ctrl+G (Might be different in your program)
8. Make sure your hex editor is set to OVERWRITE and NOT insert.
9. Replace the colors as shown in ‘Metro Customization – Hex Table.txt’ with your own. The format is Red, Green, Blue, Alpha (RGBA). For a solid/opaque image leave the last byte as FF (example: FF0000FF would be solid red)
11. In system32 rename uxtheme.dll to uxtheme.dll.old
12. Place copy the uxtheme.dll from your desktop to system32.
You can download files here.
More details on this post here.