Colorer une cellule selon condition

Sub Calcul_Date_Couleur()
    Dim Plage As Range
    Dim sh1 As Worksheet
    Dim sh2 As Worksheet
    
    Set sh1 = Worksheets("feuil1")
    Set sh2 = Worksheets("feuil2")
    With sh1
        derlig = .Range("D" & .Rows.Count).End(xlUp).Row        'derniere cellule non vide colonne A
        Set Plage = .Range("D1:D" & derlig)                     'mise en memoire plage de cellules
        nb1 = Application.CountIf(Plage, "0*")                   'nombre de fois "0" et lettre
        If nb1 > 0 Then
            ligsh1 = 1
            For n = 1 To nb1
                If n > 1 Then
                    ligsh1 = .Columns(4).Find("0*", .Cells(ligsh1, 4), , xlWhole).Row
                Else        'pour cellule ligne 1
                    If .Cells(1, 4) Like "0*" Then
                        ligsh1 = 1
                    End If
                End If
                VLsh1D = .Cells(ligsh1, 4)
                VLsh1A = .Cells(ligsh1, 1)
                With sh2
                    nb2 = Application.CountIf(.Columns(1), VLsh1D)
                    If nb2 > 0 Then
                        If .Cells(1, 1) = VLsh1D Then
                            ligsh2 = 1
                        Else
                            ligsh2 = .Columns(1).Find(VLsh1D, .Cells(1, 1), , xlWhole).Row
                        End If
                        VLsh2 = .Cells(ligsh2, 3)
                        If IsDate(VLsh1A) And IsNumeric(VLsh2) Then
                            sh1.Cells(ligsh1, 9) = VLsh1A + VLsh2
                        End If
                    Else
                        sh1.Cells(ligsh1, 4).Interior.Color = vbRed
                    End If
                End With
            Next n
        End If
    End With
    Set Plage = Nothing
End Sub