[Python] Can't set the transparency of models

When I reproduced gcs-science-robotics in the latest version of drake and ran prm_comparison.ipynb, I met this problem.

RuntimeError Traceback (most recent call last)
/tmp/ipykernel_16980/4066659220.py in <module>
----> 1 visualize_trajectory(meshcat, [linear_gcs_traj],
2 show_path=True,
3 robot_configurations=execute_task,
4 transparency=0.3)

~/lhc-gcs-science-robotics/reproduction/prm_comparison/helpers.py in visualize_trajectory(meshcat, trajectories, show_path, robot_configurations, transparency, regions)
246
247 # Set transparency of main arm and gripper.
--> 248 set_transparency_of_models(plant,
249 [iiwa.model_instance, wsg.model_instance],
250 transparency, scene_graph)

~/lhc-gcs-science-robotics/reproduction/prm_comparison/helpers.py in set_transparency_of_models(plant, model_instances, alpha, scene_graph)
122 Role.kIllustration):
123 properties = inspector.GetIllustrationProperties(geometry_id)
--> 124 phong = properties.GetProperty("phong", "diffuse")
125 phong.set(phong.r(), phong.g(), phong.b(), alpha)
126 properties.UpdateProperty("phong", "diffuse", phong)

RuntimeError: GetProperty(): Trying to read property ('phong', 'diffuse'), but the group does not exist.


then I found that properties group name was '__default__'. I want to know that if API changed what should I do to change the transparency of models.

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