in mujoco_worldgen/util/sim_funcs.py [0:0]
def change_geom_alpha(model, body_name_prefix, new_alpha):
''' Changes the visual transparency (alpha) of an object'''
for body_name in model.body_names:
if body_name.startswith(body_name_prefix):
for geom_id in get_body_geom_ids(model, body_name):
model.geom_rgba[geom_id, 3] = new_alpha