Crop texture of 3D-object

I've got a diver with a depth finder which ranges from green to red (see picture).
I'd like to crop that texture on the fly so I can determine the shown amount of the bar myself.

How can I proceed to make this work?

This code from the unity-documentation using SetPixels() didn't work at all.

Code (csharp):

1. exture2D sourceTex = renderer.material.mainTexture as Texture2D;
2.         int x = 50;
3.         int y = 30;
4.         int width = 100;
5.         int height = 100;
6.         Color[] pix = sourceTex.GetPixels(x, y, width, height);
7.         Texture2D destTex = new Texture2D(width, height);
8.         destTex.SetPixels(pix);
9.         destTex.Apply();
10.         renderer.material.mainTexture = destTex;

 

You probably want to tweak the tiling and offset values of the material, which determine what part of the texture are shown.

 

That only amounts to moving or resizing the texture, not cropping though.