The way we've always played is that
1) For a single action, all coloured citizens go on the same building and in the case of a hospital you have to choose either health or education at this point. I think this is why it says arch (curve) rather than building - otherwise it would be ambiguous for the hospital.
I'm not sure about this interpretation.
Check this forum: http://www.boardgamegeek.com/thread/136808