Sub test()
Dim n, i As Integer
n = InputBox("Number of subscribers", "Set background color")
If n = vbNullString Then
Exit Sub
Else
For i = 1 To Round(Columns("A").Cells(Rows.Count).End(xlUp).Row / n, 0)
Range("A" & (2 + n * i - n) & ":A" & (n * i + 1)).Interior.ColorIndex = i + 2
Next i
End If
End Sub