I am attaching the ComboBox.xaml file applied in a project. In the NonEditable RadComboBox template there is a ButtonChrome control that does not have its Background property TemplateBound by default. If you do bind it you can use the Background property on both editable and non editable combo.
It is a little frustrating but the Background of editable combo is white while that on a non editable is grayscale so we can not have the backgrounds in both the templates TemplateBound to the RadComboBox's Background.
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