In order to achieve the desired I can suggest you two different approaches. First one is to change the EffectLowColor
of the Office2013 theme - it will change the color of the selected Appointments, but it will also affect the colors of other ScheduleView elements. You can do it the following way:
Office2013Palette.Palette.EffectLowColor = Colors.Orange;
For more details about styling the Office2013 theme you can check this article
from our online help documentation.
The second approach is to extract and modify the default AppointmentItemVertical and AppointmentItemHorizontal ControlTemplates in order to change the color of the Border named SelectionVisual. Afterwards you would need to apply the templates using the AppointmentStyleSelector
Hope this helps. If you have any further questions let us know.
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