Based on this answer by @Ilya, I have created this code:
var event = CalendarApp.getCalendarById(calendarid).createEvent(
eventtitle,
startfull,
endfull,
{description: eventdescription,
location: eventaddress}
);
event.id = event.getId();
event.colorId = "#616161";
Calendar.Events.patch(event, calendarid, event.id);
Basically trying to "grey-out" some events of less importance, while leaving others in the default calendar color. This color change happens on the same execution as the actual event creation. The event is created fine, but only with the default calendar color. When the above code runs, I get an error:
Object does not allow properties to be added or changed.
I think that perhaps it has something to do with this but I'm not sure how to resolve it.
For future reference by other users, here's the best list of colors I could find as of now.