MajorGridlines Property
Returns a Gridlines object that represents the major gridlines for the specified axis. Only axes in the primary axis group can have gridlines. Read-only.
Example
This example sets the color of the major gridlines for the value axis in Chart1.
With Charts("Chart1").Axes(xlValue)
If .HasMajorGridlines Then
.MajorGridlines.Border.ColorIndex = 5 'set color to blue
End If
End With