In the initial release of Windows 8, you accessed the Colors and Accents features through PC Settings under Personalize (see below).
In Windows 8.1, Microsoft has now moved this setting to Charm bar. To access it, make sure you are in the Start Screen interface.
Press Windows key + C and click Settings or place your mouse pointer in the right hand corner and click Settings.
Click Personalize. (Note), if you do this from the Desktop, you will taking to the Desktop personalization options. So make sure you are at the Start Screen.
Choose your Background art, which are now animated. Then select a colour from the ‘Background color’ palette and then select your accent color which will be applied to the animated object, thats it. See example below: