The size of the columns already indicates that. I think varying the colors as well would be confusing.
Google "comparison chart" and see how <a href="http://www.google.com/imgres?imgurl=http://printgreener.com/... facets</a> can inform a viewer in a simple way.
2. I agree with the parent about the color coding. It might be more clear if you use a red-green spectrum for each day (e.g. red for the evening, when things might be more busy, and green for the morning, when things might be less busy).