折れ線のマーカーを丸形・8ポイントにする

Option Explicit

Sub Example5038()
    Dim ws As Worksheet, co As ChartObject
    On Error GoTo Failed
    '新しい練習シートだけを作成・変更します。
    Set ws = NewSheet5038()
    If ws Is Nothing Then Exit Sub
    Set co = ws.ChartObjects.Add(ws.Range("E2").Left, ws.Range("E2").Top, 420, 250)
    co.ShapeRange.Item(1).Name = "練習グラフ"
    co.Chart.ChartType = xlLine
    co.Chart.SetSourceData Source:=ws.Range("A1:C5"), PlotBy:=xlColumns
    'ここから今回の操作です。
    With co.Chart.SeriesCollection(1)
        .MarkerStyle = xlMarkerStyleCircle
        .MarkerSize = 8
        .MarkerForegroundColor = RGB(42, 105, 180)
        .MarkerBackgroundColor = RGB(255, 255, 255)
    End With
    Exit Sub
Failed:
    MsgBox "処理を中止しました: " & Err.Description, vbExclamation
End Sub

Private Function NewSheet5038() As Worksheet
    Const SHEET_NAME As String = "VBAグラフ5038"
    Dim item As Object, ws As Worksheet
    Dim data As Variant, r As Long, c As Long
    '同名シートがあれば、上書きせずに終了します。
    For Each item In ThisWorkbook.Sheets
        If StrComp(item.Name, SHEET_NAME, vbTextCompare) = 0 Then
            MsgBox SHEET_NAME & " は既にあります。別の練習ブックで試してください。"
            Exit Function
        End If
    Next item
    Set ws = ThisWorkbook.Worksheets.Add( _
        After:=ThisWorkbook.Sheets(ThisWorkbook.Sheets.Count))
    ws.Name = SHEET_NAME
    data = Array(Array("月", "売上", "計画"), _
                 Array("4月", 120, 100), Array("5月", 160, 140), _
                 Array("6月", 110, 150), Array("7月", 180, 170))
    For r = 0 To UBound(data)
        For c = 0 To UBound(data(r))
            ws.Cells(r + 1, c + 1).Value = data(r)(c)
        Next c
    Next r
    ws.Range("A1:C5").Columns.AutoFit
    Set NewSheet5038 = ws
End Function