SolidWorks API C# Body Transparency

Hello, guys. I'm working with SolidWorks plug-in. I need to create transparent body, but I can't do it. Can someone help me ??
I create new body by IModeler class, like this:

        protected virtual IBody2[] OnCreateBodies(ISldWokrs application, IModelDoc2 document, DetectorMacroFeatureData properties)

        {

            double halfWidthX = (double)properties["X Half Width"].Value;

            double halfWidthY = (double)properties["Y Half Width"].Value;

            IModeler modeler = application.IGetModeler();

            IPartDoc part = document as IPartDoc;

            Point3D[] points = new Point3D[] { new Point3D(-halfWidthX, -halfWidthY, 0.5), new Point3D(-halfWidthX, halfWidthY, 0.5),

                                               new Point3D(halfWidthX, halfWidthY, 0.5), new Point3D(halfWidthX, -halfWidthY, 0.5) };

            Curve[] border = new Curve[4];

            for (int i = 0; i < 4; i++)

            {

                border[i] = SWGeometry.CreateLine(application, points[i], points[(i + 1) % 4]);

            }

            Surface planeSurf = modeler.CreatePlanarSurface2(new double[] { 0, 0, 0.5 }, new double[] { 0, 0, 1 }, new double[] { 1, 0, 0 }) as Surface;

            IBody2 detectorBody = planeSurf.CreateTrimmedSheet4(border, true) as IBody2;        

            return new IBody2[] { detectorBody };

        }

When i use this function, i create correct planar body. Now i need to do it invisible (not hiden). So i want to set transparent as 100 %.
I reed, that i can do it by using MaterialPropertyValues2 property. But it is not work for me. When i try to get or set it, it always equals NULL.

var material = detectorBody.MaterialPropertyValues2 as double[]; // return NULL, like double[] or like object, anyway it equals NULL

material[7] = 1.0;

detectorBody.MaterialPropertyValues2 = material; // still equals NULL

Can someone help me or show some offers ?? I'm begginer in work with SolidWorks API, so it will be nice, if you show me some examples.

SolidworksApi macros