I'd like to define tags or keywords and associate them with a color in my calendar. For example if I have a calendar entry that has the title "Drop off #kids" it would be colored green because of the tag #kids. If there is an entry such as "#meeting for lunch with Silvio" it would be colored yellow because of #meeting and so on.
The tags could be in the title or in the body.

This would also allow a very easy synchronization of colors for shared calendars, because you only have to share the coloring rules for each party and then the colors are applied automatically.