I will get straight to your questions.
Unfortunately, we were not able to reproduce the issue you've encountered. Please find attached a sample file. You can compare it with your project. If you still have any problems you can send us the your project.
In order to change the background color of the RadMap control you have to set property Background of the RadMap.
RadMap1.Background = new SolidColorBrush(Colors.Red);
If you have further questions please do not hesitate to ask us.
I hope this will help you.
the Telerik team
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