Generally styles used in our themes are theme specific. When you predefine the template using Microsoft Expression Blend, you get the style against the default Office_Black theme. As you may know we ship our themes as separate projects and you may get the styles for all components from the Themes folder of your personal installation. If you want to modify the style of RadDataPager against Metro theme you should go to the Metro project within Themes folder and copy the style of RadDataPager to your own project. Once you have the default Metro template in your project you should modify the MainBrush color, which is the brush resource used to paint the Background of RadDataPager.
Please give it a try and if you need any further assistance do not hesitate to contact us!
All the best,
the Telerik team