Here’s a quick VBA macro for removing axis gridlines and greying out all the lines in an Excel plot.

This relates to the post Drawing Better Graphs – Have Your Data Tell the Story

Sub GreyLines()

    For Each axs In ActiveChart.Axes
        axs.HasMajorGridlines = False
        axs.HasMinorGridlines = False
    Next
    
    For Each srs In ActiveChart.SeriesCollection
        srs.MarkerStyle = xlMarkerStyleNone
        'srs.MarkerForegroundColor = RGB(200, 200, 170)
        'srs.MarkerBackgroundColor = RGB(170, 170, 170)
        srs.Format.Line.ForeColor.RGB = RGB(215, 215, 215)
    Next
End Sub