The only major concern I would have is that with winter approaching, people wear whatever cold weather gear they have. Most ardent Chiefs fans (i.e. the people that will still bother to show up at all) have probably put down some significant coin on red warm-weather gear.
Then again, you could always put a hefty sack over your coat...
It's doable, we just need to get the word out. If even half the crowd is wearing black one week, it will be clearly noticeable.
If you can't draw a crowd, draw dicks on the wall.