The styles of the RadPanelBar and RadPanelBarItem could be found in the Themes folder in your installation folder of RadControls or they could be extracted from ExpressionBlend. I prepared a sample for you that has these styles extracted in the Resources of the MainPage. I also edited the style of the first RadPanelBarItem in the project and these two following Colors to Transparent:
Please let us know if this helped you or not.
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