EXCEL VBA 获取特定区域内的值求和

选中一个灰色的单元格，同时按Alt和F11进入宏界面，点菜单的插入，模块，粘贴如下代码：
Sub aaa()
MsgBox Selection.Interior.ColorIndex
End Sub

直接按F5运行此宏，得到一数字，这是灰色的VBA代码，记住它。再粘贴如下代码：
Sub test()
Dim xRng, cell As Range
Dim xSum, xCount As Single
Set xRng = Cells.Find(Date)
If xRng Is Nothing Then
MsgBox "Not find today"
Else
Set xRng = xRng.Offset(2, 0).Resize(19, 8)
For Each cell In xRng
If cell.Interior.ColorIndex = 16 Then
xSum = xSum + cell
xCount = xCount + 1
End If
Next
End If
MsgBox xSum & Chr(10) & xCount
End Sub

把粗体的16改为刚才那个数字，按F5运行此宏，OK。

灰色的单元格是怎么来的？