FullCalendar Overlapping Events different color

I am using Fullcalendar / Scheduler to show some events on a calendar. I get all my information from a REST service.

I know that Fullcalendar has a method that checks if an event is overlapping with another ( it does this when using the slotEventOverlap attribute ) so that it will make it 50% or less depending on how many events there are.

My question is this, has anyone any idea what that method is .. What I need to achieve is that when two overlapping events are on the calendar, they should be in red. Something like this:

I was thinking that somewhere in the library, when the computing is done, and the % are set, a new class can be added to these events, something like fc-overlap, that I could customize.

Or does anyone have any idea on how I could achieve this?

The only solution I can find is after I get the list of events, parse them in a function check if startTime & endTime overlap and somehow assign a class to only those that overlapp. (I can identify the events via their ID ) but this seems somehow defeating the purpose since the calendar is already doing a validation when it's rendering the events.

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