With the exception of Barney and Robin, all other main characters in this episode (Ted, Marshall, Lily, Nora, Kevin) wear purple.
While Ted, Marshall, and Lily, are sitting at the concert, the people behind them are eating sandwiches like Ted and Marshall were. Of course eating sandwiches is code of smoking pot.
David Neher and Jerry Minor both have small roles in this episode. Both of whom also have recurring roles in Community (2009).