how to set the lightness of the dot

[Jeff]

You can change the vertex color of the points:

import viz
viz.go()

viz.startLayer(viz.POINTS)
viz.vertexColor(0.5,0.5,0.5)
viz.vertex(0,0,1)
viz.vertex(0,0.5,1)
aa=viz.endLayer(pos=[0,1.8,3])