function Start () {
    // Create a new 2x2 texture ARGB32 (32 bit with alpha) and no mipmaps
    var texture = new Texture2D(2, 2, TextureFormat.ARGB32, false);

    // set the pixel values
    texture.SetPixel(0, 0, Color(1.0, 1.0, 1.0, 0.5));
    texture.SetPixel(1, 0, Color.clear);
    texture.SetPixel(0, 1, Color.white);
    texture.SetPixel(1, 1, Color.black);

    // Apply all SetPixel calls
    texture.Apply();

    // connect texture to material of GameObject this script is attached to
    renderer.material.mainTexture = texture;
}