MainWindow.xaml

<dx:ThemedWindow x:Class="CustomAppointmentBackground.MainWindow"
                 xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                 xmlns:dx="http://schemas.devexpress.com/winfx/2008/xaml/core"
                 xmlns:dxmvvm="http://schemas.devexpress.com/winfx/2008/xaml/mvvm"
                 xmlns:dxsch="http://schemas.devexpress.com/winfx/2008/xaml/scheduling"
                 xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                 xmlns:local="clr-namespace:CustomAppointmentBackground"
                 Title="MainWindow" Height="550" Width="825"
                 DataContext="{dxmvvm:ViewModelSource local:MainViewModel}">
    <Grid>

        <dxsch:SchedulerControl x:Name="scheduler" CommandBarStyle="Ribbon" 
                                GroupType="Resource" 
                                FirstDayOfWeek="Monday"                                 
                                ActiveViewIndex="0" CustomAppointmentBackground="SchedulerControl_CustomAppointmentBackground">
            <dxsch:DayView x:Name="dayView1" DayCount="2" ResourcesPerPage="2" TopRowTime="9:0:0"/>
            <dxsch:SchedulerControl.DataSource>
                <dxsch:DataSource AppointmentsSource="{Binding Appointments}" ResourcesSource="{Binding Doctors}">
                    <dxsch:DataSource.AppointmentMappings>
                        <dxsch:AppointmentMappings AllDay="AllDay"
                                                   Id="Id"
                                                   End="EndTime"
                                                   LabelId="IssueId"
                                                   Location="Location"
                                                   RecurrenceInfo="RecurrenceInfo"
                                                   Reminder="ReminderInfo"
                                                   ResourceId="DoctorId"
                                                   Start="StartTime"
                                                   StatusId="PaymentStateId"
                                                   Subject="PatientName"
                                                   Type="Type">
                            <dxsch:CustomFieldMapping Mapping="InsuranceNumber" Name="InsuranceNumber" />
                            <dxsch:CustomFieldMapping Mapping="FirstVisit" Name="FirstVisit" />
                            <dxsch:CustomFieldMapping Mapping="Notes" Name="Notes" />
                        </dxsch:AppointmentMappings>
                    </dxsch:DataSource.AppointmentMappings>
                    <dxsch:DataSource.ResourceMappings>
                        <dxsch:ResourceMappings Caption="Name" Id="Id" />
                    </dxsch:DataSource.ResourceMappings>
                </dxsch:DataSource>
            </dxsch:SchedulerControl.DataSource>
        </dxsch:SchedulerControl>

    </Grid>
</dx:ThemedWindow>