Different color for each lever of the surface chart

I’m trying to break chart (Z axis) into zones with different color.
For example, in the following code I use GridDataSeries.ContourData property to the color to range from 0 to 0.2 changed from color1 to color2, and so on. I don’t get it

c1Chart3D1.ChartType = Chart3DType.SurfaceZone;
var ds = new GridDataSeries();
ds.Start = new Point(-1, -1); // start for x,y
ds.Step = new Point(stepx, stepy); // step for x,y
ds.ZData = zdata; // z-values
double[,] d = new double[2, 2];
d[0, 0] = 0.2;
d[0, 1] = 0.5;
d[1, 0] = 0.75;
d[1, 1] = 1.0;

ds.ContourData = d;

c1Chart3D1.Children.Add(ds);