windows 8
When customizing your theme, you can choose to have Windows automatically set colors. It seems to change automatically based on the background you choose. How does this work? Does it sense which colors are in your background image and do color math to figure out what the theme should be?
Use ModernBack Changer:
It works with Windows 8 RTM and lets you change both the background and accent color.
I finally found the solution!
All the required information can be found on this page:
http://code-bude.net/2012/08/31/anleitung-benutzerdefinierte-hintergrundbilder-in-windows-8/(German)
Basically the new file containing the images is imageres.dll. Opening it with ResourceHacker reveals all the wallpapers in the PNG section.
The backgrounds begin with Resource 10000. For each pattern(and some colors?) there are 5 images each.
For example exporting 10003 creates a 3000x800px PNG:
Best Answer
They analyze the desktop background image and select the color which used the most in the image.
It works the same way as Taskbar button highlights with the icon color in Windows 7 and 8.