Setting properties is not sufficient to achieve all design details. Although the controls have properties such as BorderBrush Background and Foreground their templates use several visual elements with 2 or 3 borders, shadows, areas with different background colors and states. There is no MouseOverBackground or something like that so if you want to style the menu you will have to edit the menu's template.
Editing the colors used in the templates for state effects in Expression Blend should be quite easy.
Please refer to this forum discussion
for more information about editing the RadMenu hover colour. It is for Silverlight, but the same principles apply for WPF.
the Telerik team
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