Create a Unity Mesh with 2 triangles

triangles2.cs

// Creating Mesh data in Unity
// This script should be attached to an empty GameObject.  It requires vertexColor.shader (https://gist.github.com/davepape/0dee3b1550a1f4159bc173e1b32dbe0c)
// On startup, it will create a MeshFilter containing 2 triangles, and apply a Material.
using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class triangles2 : MonoBehaviour {

  void Start ()
    {
    gameObject.AddComponent<MeshFilter>();
    gameObject.AddComponent<MeshRenderer>();
    Material mat = new Material(Shader.Find("Custom/Vertex Colored"));
    GetComponent<Renderer>().material = mat;
    Vector3[] newVertices = { new Vector3(-2f,0f,-1f), new Vector3(0f,1f,-1f), new Vector3(1f,0f,-1f), new Vector3(0f,-1f,-1f) };
    Color[] newColors = { Color.red, Color.green, Color.blue, Color.yellow };
    int[] newTriangles = { 0,1,2, 0,2,3 };
    Mesh m = GetComponent<MeshFilter>().mesh;
    m.vertices = newVertices;
    m.colors = newColors;
    m.triangles = newTriangles;
    }
    
  void Update ()
    {
    }
}