Hello ksk,
RadPanelBar and the all corresponding PanelBarGroupElements should have theme by default. You can change theme, by changing the ThemeName property. This actually is valid for all RadControls. You can find more on the topic here:
http://www.telerik.com/help/winforms/themes_using_default_themes_.html
If this does not help, can you please specify in more details what you need to achieve?
All the best,
Mike
the Telerik team