To reset the marker color with the current implementation, you can create two script notifiers under an event rule.
The first script notifier runs when event starts or is pending (by checking "Start" and "Pending" options in "Run this when" dropdown) and it sets the marker color.
The second one is set to be executed when event finishes, and it also sets the marker color, but to a default color (e.g. Map.setMarkerColor('000000'); to set it black).
P.S. We are aware that the initial marker color might be something different than black. Therefore, we will consider implementing a new function which resets the marker color to its initial state.