For i3 = 13 To Len(c3)

For i3 = 1 To Len(c3)

    For i3 = 1 To Len(c3)
        If IsNumeric(Mid(c3, i3, 1)) Then
            c3.Characters(Start:=i3, Length:=1).Font.ColorIndex = 3
        End If
    Next i3

Sub ShowCifer()
    Application.ScreenUpdating = False
    With CreateObject("VBScript.Regexp")
        .Global = True
        .Ignorecase = True
        .Pattern = "[0-9]"
        For Each c In Selection.SpecialCells(xlCellTypeConstants, 23)
            h = Len(c)
            d = h - Len(.Replace(c, ""))
            If d > 0 Then
                g = 1
                i = .Replace(c, 0)
                For e = 1 To d
                    g = InStr(Mid(i, g, h), 0) + g
                    c.Characters(Start:=g - 1, Length:=1).Font.ColorIndex = 3
                Next
            End If
        Next
    End With
End Sub

For i3 = 1 To Len(c3)