When using the pythreejs backend, only the first shape of a primitive is drawn, and it's solid black.
I saw this issue with @k-l-wang the other day and it's occurring on my machine too.

Version information:

• plato from master branch (156bc56, also tested an older commit, 975c704)
• pythreejs=2.0.2=py36_1000

Code to reproduce, in a Jupyter notebook:

import plato.draw.fresnel as draw
import numpy as np
positions = np.zeros((10, 3))
positions[:, 0] = np.arange(10)
positions -= np.mean(positions, axis=0)
spheres = draw.Spheres(positions=positions)
scene = draw.Scene(spheres)
scene.show()

fresnel backend output:

pythreejs backend output (it appears to be drawing either the first or the last shape - the one on the right side is drawn in this case).