Mesh texture not properly rendered

Hello, I am creating random shapes by code and trying to texture them.. I ended up with this :

You can see there that my shape is divided into several triangles forming a hexagon..

It is created by taking a mesh from a cube, its uv, normals and so on, and then I substitute the vertices, triangles ,etc

I did that (taking it from a cube) because otherwise nothing was shown on the surface...but still something is not quite right, as you can see there are some triangles in my mesh that do not have a texture...

Can anyone help me find out why these triangles in particular do not get textured?

Thanks!

This is my source code :

public class Tetrahedron : MonoBehaviour { List vertices = new List(); List triangles = new List(); List uv = new List(); List normals = new List(); List colors = new List();

         public bool sharedVertices = false;
     
         public void Build(Center c){
         GameObject cube = GameObject.Find("Cube");
         Mesh mesh =  cube.GetComponent<MeshFilter>().mesh;
         MeshFilter meshFilter = GetComponent<MeshFilter>();
         var mesh2 = meshFilter.sharedMesh;
         meshFilter.sharedMesh = mesh;
         MeshRenderer renderer = (MeshRenderer) meshFilter.renderer;



         //var sha = Shader.Find ("Diffuse");
         
         //Material mat = new Material( sha);
         var mat =  Resources.Load("materials/Terrain",typeof(Material)) as Material;
         renderer.material = mat;

       
              
         mesh.colors = colors.ToArray();
         foreach (Triangle t in c.Polygon.tris) {
             t.vertices.Select(b => b.Position).ToList().ForEach(x => vertices.Add(x));
         }
         mesh.triangles = new int[]{};
         mesh.vertices = new Vector3[]{};
         mesh.vertices = vertices.ToArray();


         //mat.color = c.Biome.Color;
         vertices.ForEach(b => colors.Add(c.Biome.Color));

         System.Random rand = new System.Random();

         triangles = new List<int>();
         int i = vertices.Count -1;
          
         foreach( var v in vertices)
         {
             triangles.Add(i);
             i--;
         }
         mesh.triangles = triangles.ToArray();
         uv = new  List<Vector2>();
         vertices.ForEach(b => uv.Add( new Vector2(0f,0f)));
             // basically just assigns a corner of the texture to each vertex

         mesh.uv =  uv.ToArray();//new Vector2[vertices.Count];// uv.ToArray();


         vertices.ForEach(b => normals.Add( c.Normal));
            
         mesh.normals = normals.ToArray();
         //mesh.RecalculateNormals();
         mesh.RecalculateBounds();
         mesh.Optimize();
     }
     // Use this for initialization
     void Start () {
     
     }
     
     // Update is called once per frame
     void Update () {
     }

}