Problems in land generation with SetPixel () function;

Hello, I would like to know how can I generate a ground (not heightmap, land) of pixels with SetPixel function (int, int, color);?
I already tried, but all I can and fill half of texture in green, the problem yourself and to generate reliefs and mountains, can someone help me?
That is your current code with problems:

Code (JavaScript):

1.  
2. #pragma strict
3.  
4. var Terrain: Texture2D = new Texture2D(100,100);
5. var Pixel: Color;
6. var X: float;
7. var Y: float;
8. var Perlin: float;
9. var PerlinFactor: int;
10. var PerlinI: int;
11. var Material: Material;
12. var Seed: float = 0;
13.  
14.  
15. function Start () {
16. for(X = 0; X < Terrain.height; X++)
17.    for(Y = 0; Y < Terrain.width; Y++)
18.    {
19.    Terrain.SetPixel(X,Y,Color.clear);
20.    }
21.    Terrain.Apply();
22. for(X = 0; X < Terrain.height; X++)
23.    for(Y = 0; Y < 500; Y++)
24.    {
25.    Perlin = PerlinFactor*Mathf.PerlinNoise(Random.Range(0.0,0.5),Random.Range(0.6,1.0));
26.    PerlinI = Mathf.FloorToInt(Perlin);
27.    PerlinI = Random.Range(Y+1,Y+100);
28.    Terrain.SetPixel(X,Y+PerlinI,Pixel);
29.    }
30.    Terrain.Apply();
31.    Material.mainTexture = Terrain;
32.    print("The Map Has Sucefully Generated!!!");
33. }

And then, someone help me?