Generating a triangle from 3 points

From the official docs on meshes

 // Builds a mesh containing a single triangle with uv's.
 function Start () {
     gameObject.AddComponent("MeshFilter");
     gameObject.AddComponent("MeshRenderer");
     var mesh : Mesh = GetComponent(MeshFilter).mesh;
     mesh.Clear();
     mesh.vertices = [Vector3(0,0,0), Vector3(0,1,0), Vector3(1, 1, 0)];
     mesh.uv = [Vector2 (0, 0), Vector2 (0, 1), Vector2 (1, 1)];
     mesh.triangles = [0, 1, 2];
 }

...and then the official docs on materials has an example for setting material color

If you want to play in the OpenGL style, use the GL class to draw the triangle - there's a very useful example in this topic.

But if you want to create a game object with a simple triangular mesh, take a look at the mesh topic in the Unity manual, or at the Mesh class in the docs - both have useful examples, and the later allows selection of C# language.

Here you can learn step by step how to draw a triangle just by code (Turn on English subtitles) https://www.youtube.com/watch?v=ThWyvoqWjhE&list=PLp2zpxnnEFuemzgoUFYGkKQWwygDFXiIt![alt text][1]

[1]: /storage/temp/148854-triangle-unity.png

Make a triangle I'm blender then export to unity and turn off the mesh renderer. Simply solution

Well, I not so recommended way, but a way you can generate a triangle is using calls to OpenGL directly:

 GL.Begin( GL.TRIANGLES);
 GL.Color( Color(1,1,1,1) );
 GL.Vertex3( 0, 0, 1 );
 GL.Vertex3( 1, 0, 1 );
 GL.Vertex3( 0, 1, 1 );
 GL.End();

Something to that effect, do some googling and you will find plenty of resources on OpenGL.

But, to make a GameObject that will rotate, scale and do everything you want, and have a triangle shape, you would be best off making the object in something like Blender.