Rectangles are not drawn of specified Colors !!!!

I need to draw N vertical parts. So, I draw rectangles specifying its parameters & different colors for each part.

        private void DrawSections()
        {
            double x = 0, y = 0;
            int i=0;
            SolidColorBrush[] brushes = new SolidColorBrush[]{Brushes.Red, Brushes.Purple, Brushes.Gold, Brushes.Green, Brushes.YellowGreen, Brushes.Turquoise, Brushes.Wheat, Brushes.Pink, Brushes.PaleVioletRed, Brushes.Olive};

            foreach (Section sec in areasList_Scaled)
            {
                RectangleVisual3D rect = new RectangleVisual3D();
                rect.Origin = new Point3D(x, y, 0);
                rect.Length = 120;
                rect.Width = sec.Length;   // myRect.Width;
                //rect.Fill = Brushes.Lavender;   // new SolidColorBrush(Colors.LightCoral);
                rect.Material = new DiffuseMaterial(brushes[i]);
                i++;

                Console.Write("RECT LEN = " + sec.Length);

                y += sec.Length;
                wellViewport.Children.Add(rect);
            }
        }

With this code, I get rectangles, but not of the specified colors - instead of black & white colors. The Length of each sections is like
RECT LEN = 12.2586666666667RECT LEN = 0.202133333333333RECT LEN = 11.5825333333333RECT LEN = 0.157333333333333RECT LEN = 19.9297333333333RECT LEN = 0.15733333333333RECT LEN = 17.8796666666667RECT LEN = 0.157399999999992

I know I have set rect.Width = sec.Length which sould be set for rect.Length. But with that setting, I was getting rectangle vertically long the length is smaller than width. I couldn't get why was getting that results also.

Any idea, why the rectangles are not shown of specified colors and of black & white colors !!!!
This is mainly to get the background effect. Each section tells something different.

Any help is highly appreciated.

Thanks

Did you add lights to your scene?

Oh yes, I hadn't added lights. Had no idea that, without lights 3D colors are not visible !!!!.

Added lights and now it shows properly.

I need to add background to rectangles of image. Can you suggest any link or article that can help me or you provide an example for the same.

Thanks a lot.