VBA 按列查找小工具类似lookUp函数

如上图，查找A列的数据在D,F列是否存在，如果存在背景色变绿，如果不存在则A列的背景色变红。

直接贴上代码：

 Private Sub CommandButton1_Click()
     Call lookUpAToDF
 End Sub

 Public Sub lookUpAToDF()
    Dim a, d, f As Long
    'Count of non-empty data in colum A,D,F
    a = Application.WorksheetFunction.CountA(Range("A:A"))
    d = Application.WorksheetFunction.CountA(Range("D:D"))
    f = Application.WorksheetFunction.CountA(Range("F:F"))
    Dim ac, dc, fc As Integer
    'loop the A
    For ac =  To a Step
        Dim aTxt As String
        ' get column A value
        aTxt = TrimSpace(Cells(ac, ).Text)
        If aTxt = "" Then
            Exit For
        End If
        ' add flg var for switch selected aTxt
        Dim flg As Boolean
        flg = True
        For dc =  To d Step
            Dim dTxt As String
            dTxt = TrimSpace(Cells(dc, ).Text)
            If aTxt = dTxt Then
                flg = False
                Exit For
            End If
        Next dc
        'if column D selected result is empty then
        'loop the colum F
        If flg Then
            For fc =  To f Step
                Dim fTxt As String
                fTxt = TrimSpace(Cells(fc, ).Text)
                If aTxt = fTxt Then
                    flg = False
                    Exit For
                End If
            Next fc
        End If
        If flg Then
            Cells(ac, ).Interior.ColorIndex =  'red
        Else
            Cells(ac, ).Interior.ColorIndex =  'green
        End If
    Next ac
    MsgBox "find completed!"
 End Sub
 Public Function TrimSpace(strItem As String) As String
    Dim resultStr As String
    resultStr = LTrim(strItem)
    resultStr = RTrim(resultStr)
    TrimSpace = resultStr
 End Function

代码还没有优化，行数达到10000+的时候会有卡顿。