No color is being rendered while rendering obj file

@germanros1987 I'm using the following code to read the obj file. However, the rendered 3d object doesn't have any colors. why is that so?

```
import open3d as o3d

def visualize(mesh):
vis = o3d.visualization.Visualizer()
vis.create_window()
vis.add_geometry(mesh)
vis.run()
vis.destroy_window()

mesh_o3d = o3d.io.read_triangle_mesh("textured.obj")
```