Change Viewport Display setting programmatically

using System;
using Rhino;
using Rhino.Display;

var doc = RhinoDoc.ActiveDoc;
var displayMode = doc.Views.Find("Perspective", false).ActiveViewport.DisplayMode;

displayMode.DisplayAttributes.FillMode = DisplayPipelineAttributes.FrameBufferFillMode.Gradient2Color;
DisplayModeDescription.UpdateDisplayMode(displayMode);