We using MASON to try and simulate a traffic scenario where cars and traffic lights are agents, and we would like to be able to update the color of the traffic lights during the simulation.  Is there any way to update the portrayal as the simulation is running?  Or perhaps add and remove agents as the simulation is running?  We would really like to use setupPortrayals() to setup the initial portrayal and then update the portrayal each step.

Thanks very much!