public CalendarControl CalendarFrom { get; }

Public ReadOnly Property CalendarFrom As CalendarControl

using DevExpress.DashboardWin;
using DevExpress.XtraEditors.Controls;
using System;
using System.Collections.Generic;
using System.Data;
using System.Drawing;
using System.Linq;
// ...
    dashboardViewer1.DashboardItemControlCreated += DashboardViewer1_DashboardItemControlCreated;
// ...
    private void DashboardViewer1_DashboardItemControlCreated(object sender, DashboardItemControlEventArgs e)
    {
        if (e.DateFilterControl != null)
        {
            e.DateFilterControl.CalendarFrom.CustomDrawDayNumberCell += Calendar_CustomDrawDayNumberCell;
            e.DateFilterControl.CalendarTo.CustomDrawDayNumberCell += Calendar_CustomDrawDayNumberCell;
        }
    }

    DateTime minValue;
    DateTime maxValue;

    private void Calendar_CustomDrawDayNumberCell(object sender, DevExpress.XtraEditors.Calendar.CustomDrawDayNumberCellEventArgs e)
    {
        CalendarControl calendar = sender as CalendarControl;

        if (e.Date > minValue && e.Date < maxValue)
            e.Style.BackColor = Color.FromArgb(80, 0, 100, 10);

        if (e.Selected && e.View == DateEditCalendarViewType.MonthInfo)
        {
            StringFormat dayFormat = new StringFormat();
            dayFormat.Alignment = StringAlignment.Center;
            dayFormat.LineAlignment = StringAlignment.Center;
            Rectangle rect = e.ContentBounds;
            rect.Inflate(2, 2);
            Font cellFont = new Font(calendar.CalendarAppearance.DayCell.Font.FontFamily, calendar.CalendarAppearance.DayCell.Font.Size + 2);
            e.Cache.FillRectangle(new SolidBrush(Color.Yellow), e.ContentBounds);
            e.Cache.Graphics.DrawString($"{e.Date.Day}", cellFont, Brushes.Black, rect, dayFormat);
            e.Handled = true;
        }
    }

Imports DevExpress.DashboardWin
Imports DevExpress.XtraEditors.Controls
Imports System
Imports System.Collections.Generic
Imports System.Data
Imports System.Drawing
Imports System.Linq
' ...
    AddHandler dashboardViewer1.DashboardItemControlCreated, AddressOf DashboardViewer1_DashboardItemControlCreated
' ...
    Private Sub DashboardViewer1_DashboardItemControlCreated(ByVal sender As Object, ByVal e As DevExpress.DashboardWin.DashboardItemControlEventArgs)
        If e.DateFilterControl IsNot Nothing Then
            AddHandler e.DateFilterControl.CalendarFrom.CustomDrawDayNumberCell, AddressOf Calendar_CustomDrawDayNumberCell
            AddHandler e.DateFilterControl.CalendarTo.CustomDrawDayNumberCell, AddressOf Calendar_CustomDrawDayNumberCell
        End If
    End Sub

    Private minValue As Date
    Private maxValue As Date

    Private Sub Calendar_CustomDrawDayNumberCell(ByVal sender As Object, ByVal e As DevExpress.XtraEditors.Calendar.CustomDrawDayNumberCellEventArgs)
    Dim calendar As CalendarControl = TryCast(sender, CalendarControl)

    If e.Date > minValue AndAlso e.Date < maxValue Then
        e.Style.BackColor = Color.FromArgb(80, 0, 100, 10)
    End If

    If e.Selected AndAlso e.View = DateEditCalendarViewType.MonthInfo Then
        Dim dayFormat As New StringFormat()
        dayFormat.Alignment = StringAlignment.Center
        dayFormat.LineAlignment = StringAlignment.Center
        Dim rect As Rectangle = e.ContentBounds
        rect.Inflate(2, 2)
        Dim cellFont As New Font(calendar.CalendarAppearance.DayCell.Font.FontFamily, calendar.CalendarAppearance.DayCell.Font.Size + 2)
        e.Cache.FillRectangle(New SolidBrush(Color.Yellow), e.ContentBounds)
        e.Cache.Graphics.DrawString($"{e.Date.Day}", cellFont, Brushes.Black, rect, dayFormat)
        e.Handled = True
    End If
End Sub