Highlight vs colour print...
All I know is that when you have an event that has a discrete start/finish time, then it is presented as colour print ("month view"). An event such as say "Bank Holiday" which doesn't have start/finish times on a day, will then appear highlighted. On a "week view", the difference is shown with the the "continuous" event listed on the day's header.
But you probably already know all this.
GCal + GDocs are an excellent way of sharing calendar and docs. Works wonders with my gal, family, friends n colleagues.