Thank you for contacting us.
Indeed, there are some additional steps which you should follow and which are not included in our documentation. We will update it in one of our next releases.
You should set the BackColors of the RadMenu's (and its main RadMenuItems) FillPrimitive to Transparent. This could be done in the theme using our Visual Style Builder tool. For more information about it, please refer to these videos: video1
You can set these properties programmatically as well. For this purpose, our RadControlSpy will be of good use, since it will give you more information about which visual element is which in the control's hierarchy. For more information, refer to this video
I am attaching a sample project to demonstrate the programmatic approach. If you need additional assistance, feel free to contact me.
the Telerik team
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