Please, correct me if I am wrong, but from what you explained, I understand that you wish to apply a different background color to the menu item when the menu item is enabled or disbaled.
If that is the case, then the most simple solution would be for you to use an ItemContainerStyle for the RadMenu and edit its visual states. Simply adjust the disabled state to reflect the background you wish. No additional code needed.
If this is not part of your scenario, I belive you will most probably need a solution where you apply a boolean-to-brush converter. If so, please share more details on your case.
the Telerik team
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