This command is part of the On-The-Fly family of commands. Use this family of commands to build your own On-The-Fly OpenGL based primitives that get added to your scene. It must be called within the
<viz>.startLayer and
<viz>.endLayer commands. Call this command to add a vertex to the current layer type.
viz.startLayer(viz.POINTS)
viz.vertexColor(1,0,0)
viz.vertex(0,1,0) # A red point at [0,1,0].
viz.endLayer()