Yes, it's a workbook open event. Details can be read here to implement it for yourself:

Workbook Open Event

I read that & built this - but it still does not work on entering the Work Book

What did I code wrong?

Sorry for so many questions - Thanks for your help

Private Sub Workbook_Open()

Dim lr As Long, i As Long

lr = Cells(Rows.Count, "A").End(xlUp).Row

lr = lr - 2

For i = 4 To lr Step 6

If Cells(i, 3) = Cells(i, 7) And Cells(i, 3) = Cells(i, 11) Then

Cells(i, 3).Interior.ColorIndex = 3

Cells(i, 7).Interior.ColorIndex = 3

Cells(i, 11).Interior.ColorIndex = 3

ElseIf Cells(i, 3) = Cells(i, 7) Then

Cells(i, 3).Interior.ColorIndex = 3

Cells(i, 7).Interior.ColorIndex = 3

ElseIf Cells(i, 3) = Cells(i, 11) Then

Cells(i, 3).Interior.ColorIndex = 3

Cells(i, 11).Interior.ColorIndex = 3

ElseIf Cells(i, 7) = Cells(i, 11) Then

Cells(i, 7).Interior.ColorIndex = 3

Cells(i, 11).Interior.ColorIndex = 3

End If

Next i

End Sub