Raycast on Nonconvex MeshCollider

Hey there,

Iam am trying to use a Raycast for some color Picking.

First I Generate a Mesh with Mesh Collider and Mesh Renderer from Vertices.

     public Color colorBoring;
     public Color colorAngry;
     public Color colorHappy;
     Texture2D mainTexture;
 
     private Vector3[] Vertices = { new Vector3(-1,0,0), new Vector3(0,0.5f,0), new Vector3(0,1,0), new Vector3(1,0,0)};
     private int[] Indices = { 0, 1, 2, 0, 3, 1, 3, 2, 1 };
     private Vector2[] UVs = { new Vector2(0,0), new Vector2(0.5f,0.5f), new Vector2(0.5f,1), new Vector2(1,0)};
     private List<Color> colors;
 
     // Use this for initialization
     void Start () {
 
         colors = new List<Color>();
         colors.Add(colorHappy);
         colors.Add(Color.grey);
         colors.Add(colorAngry);
         colors.Add(colorBoring);
 
         Mesh mesh = new Mesh();
         mesh.name = "Picker";
         mesh.vertices = Vertices;
         mesh.triangles = Indices;
         mesh.uv = UVs;
 
         mainTexture = new Texture2D (128, 128);
         for (int i = 0; i < mainTexture.width; i++) {
             for (int j = 0; j < mainTexture.height; j++) {
                 Color pixelColor = Color.Lerp (colorHappy, colorBoring, (float)i / mainTexture.width);
                 pixelColor = Color.Lerp (pixelColor, colorAngry, (float)j / mainTexture.height);
                 mainTexture.SetPixel (i, j, pixelColor);
             }
         }
 
         mainTexture.Apply ();
 
         GetComponent<MeshRenderer> ().material.mainTexture = mainTexture;
 
         mesh.colors = colors.ToArray();
 
         GetComponent<MeshFilter>().mesh = mesh;
         GetComponent<MeshCollider> ().sharedMesh = mesh;
         mesh.RecalculateBounds ();
         mesh.RecalculateNormals ();
     }

This is simply a Colored Triangle.

Now the other Side the Raycast. According to the Manual I need a Nonconvex Mesh Collider to use textureCoord.

 if (triggerPressed) {
             Ray ray = new Ray (transform.position, transform.forward);
             RaycastHit hit;
             var raycast = Physics.Raycast (ray, out hit);
             Debug.DrawRay (transform.position, transform.forward, Color.red);
             if (hit.collider.gameObject == Picker) {
                 Texture2D map = (Texture2D)Picker.GetComponent<MeshRenderer> ().materials[0].mainTexture;
                 var pixelUV = hit.textureCoord;
                 Debug.Log (pixelUV + " " + hit.collider.gameObject.name);
                 pixelUV.x *= map.width;
                 pixelUV.y *= map.height;
 
                 Debug.Log ("x=" + pixelUV.x + ", y=" + pixelUV.y + " " + map.GetPixel ((int)pixelUV.x, (int)pixelUV.y));
                 //Debug.Log (hit.triangleIndex);
             } else {
                 Debug.Log (hit.collider.gameObject.name);
             }
         }    

But the Raycast Ignores the MeshCollider if it is Nonconvex. If I set it Convex, it will be recognised by the Ray, but then the textureCoord is {0,0}