It would be interesting to know who the people are who designed the set and dictated the costumes, and their reasoning behind it.
Seems to me that the people of the general public (not the victims's survivors, of course) are wanting to participate in action, not grieving. Grieving was done at the National Cathedral. Now it is time to pull together and get to work.
Can you pass me the peace pipe? I'm gonna need it to get through this number.
It shows they are in mourning. Black and candles. From the comments here, it seems that way.