public class RangeAreaSeries2D :
    XYSeries2D,
    ISupportTransparency,
    ISupportSeriesBorder,
    ISupportBottomSeriesBorder,
    IGeometryHolder,
    IRangeSeriesView

Public Class RangeAreaSeries2D
    Inherits XYSeries2D
    Implements ISupportTransparency,
               ISupportSeriesBorder,
               ISupportBottomSeriesBorder,
               IGeometryHolder,
               IRangeSeriesView

<Window x:Class="RangeArea2DChart.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:dxc="http://schemas.devexpress.com/winfx/2008/xaml/charts"
        xmlns:local ="clr-namespace:RangeArea2DChart"
        Title="MainWindow" Height="350" Width="640">
    <Grid>
        <dxc:ChartControl Name="chartControl1">
            <dxc:ChartControl.DataContext>
                <local:ChartViewModel/>
            </dxc:ChartControl.DataContext>
            <dxc:ChartControl.Diagram>
                <dxc:XYDiagram2D>
                    <dxc:XYDiagram2D.Series>
                        <dxc:RangeAreaSeries2D DisplayName="Day-Night" 
                                               DataSource="{Binding DataPoints}" 
                                               ArgumentScaleType="DateTime"
                                               ArgumentDataMember="Time"
                                               ValueDataMember="Value1"
                                               dxc:RangeAreaSeries2D.Value2DataMember="Value2"
                                               Transparency="0.3" 
                                               Marker1Visible="False" Marker2Visible="False" 
                                               LabelsVisibility="True"
                                               CrosshairLabelPattern="{}{A:MMMM} D: {V1:f2} N: {V2:f2}">
                            <dxc:RangeAreaSeries2D.Label>
                                <dxc:SeriesLabel TextPattern="{}{V:f1}"/>
                            </dxc:RangeAreaSeries2D.Label>
                        </dxc:RangeAreaSeries2D>
                    </dxc:XYDiagram2D.Series>
                    <dxc:XYDiagram2D.AxisX>
                        <dxc:AxisX2D GridLinesVisible="True">
                            <dxc:AxisX2D.WholeRange>
                                <dxc:Range SideMarginsValue="10"/>
                            </dxc:AxisX2D.WholeRange>
                            <dxc:AxisX2D.Label>
                                <dxc:AxisLabel TextPattern="{}{A:MMM}"/>
                            </dxc:AxisX2D.Label>
                            <dxc:AxisX2D.DateTimeScaleOptions>
                                <dxc:ManualDateTimeScaleOptions GridSpacing="1" 
                                                                GridAlignment="Month"
                                                                AutoGrid="False"/>
                            </dxc:AxisX2D.DateTimeScaleOptions>
                        </dxc:AxisX2D>
                    </dxc:XYDiagram2D.AxisX>
                    <dxc:XYDiagram2D.AxisY>
                        <dxc:AxisY2D>
                            <dxc:AxisY2D.Title>
                                <dxc:AxisTitle Content="Temperature (&#176;C)"/>
                            </dxc:AxisY2D.Title>
                        </dxc:AxisY2D>
                    </dxc:XYDiagram2D.AxisY>
                </dxc:XYDiagram2D>
            </dxc:ChartControl.Diagram>
            <dxc:ChartControl.Titles>
                <dxc:Title Dock="Top" HorizontalAlignment="Center">Average Temperature</dxc:Title>
            </dxc:ChartControl.Titles>
        </dxc:ChartControl>
    </Grid>
</Window>

using System;
using System.Collections.Generic;
using System.Windows;
namespace RangeArea2DChart {
    //..
    public class ChartViewModel {
        List<DataPoint> dataPoints;
        public List<DataPoint> DataPoints {
            get {
                if (dataPoints == null) {
                    dataPoints = new List<DataPoint> {
                            new DataPoint (new DateTime(2019, 1, 1), 7.2, 2.7),
                            new DataPoint (new DateTime(2019, 2, 1), 8.3, 2.8),
                            new DataPoint (new DateTime(2019, 3, 1), 12.2, 5.3),
                            new DataPoint (new DateTime(2019, 4, 1), 15.6, 7.3),
                            new DataPoint (new DateTime(2019, 5, 1), 19.6, 10.9),
                            new DataPoint (new DateTime(2019, 6, 1), 22.7, 13.8),
                            new DataPoint (new DateTime(2019, 7, 1), 25.2, 15.8),
                            new DataPoint (new DateTime(2019, 8, 1), 25, 15.7),
                            new DataPoint (new DateTime(2019, 9, 1), 21.1, 12.7),
                            new DataPoint (new DateTime(2019, 10, 1), 16.3, 9.6),
                            new DataPoint (new DateTime(2019, 11, 1), 10.8, 5.8),
                            new DataPoint (new DateTime(2019, 12, 1), 7.5, 3.4)
                };
                }
                return dataPoints;
            }
        }
    }
    public class DataPoint {
        public DateTime Time { get; set; }
        public double Value1 { get; set; }
        public double Value2 { get; set; }
        public DataPoint(DateTime time, double value1, double value2) {
            this.Time = time;
            this.Value1 = value1;
            this.Value2 = value2;
        }
    }
}

Imports System
Imports System.Collections.Generic
Namespace RangeArea2DChart
    Public Class ChartViewModel
        Private f_DataPoints As List(Of DataPoint)
        Public ReadOnly Property DataPoints As List(Of DataPoint)
            Get
                If f_DataPoints Is Nothing Then
                    f_DataPoints = New List(Of DataPoint) From {
                        New DataPoint(New DateTime(2019, 1, 1), 7.2, 2.7),
                        New DataPoint(New DateTime(2019, 2, 1), 8.3, 2.8),
                        New DataPoint(New DateTime(2019, 3, 1), 12.2, 5.3),
                        New DataPoint(New DateTime(2019, 4, 1), 15.6, 7.3),
                        New DataPoint(New DateTime(2019, 5, 1), 19.6, 10.9),
                        New DataPoint(New DateTime(2019, 6, 1), 22.7, 13.8),
                        New DataPoint(New DateTime(2019, 7, 1), 25.2, 15.8),
                        New DataPoint(New DateTime(2019, 8, 1), 25, 15.7),
                        New DataPoint(New DateTime(2019, 9, 1), 21.1, 12.7),
                        New DataPoint(New DateTime(2019, 10, 1), 16.3, 9.6),
                        New DataPoint(New DateTime(2019, 11, 1), 10.8, 5.8),
                        New DataPoint(New DateTime(2019, 12, 1), 7.5, 3.4)
                    }
                End If
                Return f_DataPoints
            End Get
        End Property
    End Class
    Public Class DataPoint
        Public Property Time As Date
        Public Property Value1 As Double
        Public Property Value2 As Double
        Public Sub New(ByVal time As Date, ByVal value1 As Double, ByVal value2 As Double)
            Me.Time = time
            Me.Value1 = value1
            Me.Value2 = value2
        End Sub
    End Class
End Namespace