How to color a VoxelGrid

### Checklist

- [X] I have searched for [similar issues](https://github.com/isl-org/Open3D/issues).
- [X] For Python issues, I have tested with the [latest development wheel](http://www.open3d.org/docs/latest/getting_started.html#development-version-pip).
- [X] I have checked the [release documentation](http://www.open3d.org/docs/release/) and the [latest documentation](http://www.open3d.org/docs/latest/) (for `master` branch).

### My Question

Hi,

I'm using a VoxelGrid, I want to color some voxels in one color.

I'm using:

````python
voxel_grid_1 = o3d.geometry.VoxelGrid.create_from_triangle_mesh(hull_1,
voxel_size=1.0)
list_voxels_1 =voxel_grid_1.get_voxels()
for voxel_1 in list_voxels_1:
voxel_1.color = (1.00, 0.88, 0.30)

o3d.visualization.draw_geometries([voxel_grid_1], mesh_show_wireframe=True)
````

But when I visualize it there is no color, just my voxel grid.
Any idea?
Thanks
Kevin