I'm guessing that you have IsEditable set to false. When a ComboBox is used as a DropDown style (i.e. no edit area), then its edit area is rendered with the system highlight color when it has focus. The xamComboEditor contains a ComboBox that it uses while it is in edit mode (e.g. while it has focus) and so that is the source of the blue color you are seeing. If you want to prevent this then I believe you will need to provide a custom style for that ComboBox (e.g. by setting the ComboBoxStyle property to a custom Style that targets ComboBox). In that custom style you would need a custom Template that doesn't set this color. You can use the default xaml we ship with the product (located in the DefaultStyles directory) as a starting point for your custom template. If you search the editor's xaml for IsSelectionBoxHighlighted you should find the trigger that is causing the background/foreground change that you don't want.