Highlight day if an event takes place (event_calendar gem)


I'm busy editing the event_calendar gem a little bit so the background
of a day-number (on the displaying calendar) will turn red if an event
takes place on that day.
This is the code I have at the moment: https://gist.github.com/885960

See line #14 for the exact code to turn the background color of the
day-number to red.
I have debugged this and tested:

event and (day.to_date == dates[0])
it returned true!

So why isn't this particular day coloring red?

I have tried just putting this:
cal << %(ec-event-header )

But then all the day-numbers have a red background for the current