The Metro theme was developed with one important thing in mind - in most of the cases we have only 6 brushes for each control and they can be easily changed to create a color variation of the same theme. The default accent color indeed is blue.
You can easily change the accent color like so:
MetroColors.PaletteInstance.AccentColor = Colors.Red;
For the background color, change the MainColor:
MetroColors.PaletteInstance.MainColor = Colors.LightCoral;
The other four brushes (BasicColor, StrongColor, MarkerColor, ValidationColor) are used for different purposes across the theme, but you can experiment and see how the control changes when you change Brushes.
We are going to provide guidelines on the Metro theme in the very near future.
As a side note, the way you can view themes in the WPF onlines demos, has been changed to correspond to the one for the Silverlight online demos, which was inttroduced in 2011 Q1. It is intdended to show the theming options for a particular control in a dedicated example, thus providing for all other examples better user experience and prevent burdening the viewer with too much visual noise and distractions.
I hope this helps.
the Telerik team
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