I’ve looked at several posts about this topic, which all look closed. My request has a slightly different slant: I understand your comments on issues with this idea… what do you do when an event has multiple categories? what about days with multiple events? My idea would require adding a new field to the event: literally a calendar color/category.
My client has asked for this because prior to moving them to your plugin, we used a composite of approaches to reflect events – one of which was the Kieran O’Shea calendar (http://www.kieranoshea.com/calendar) – which got them used to the colorful display.
It’s a “nice to have” item. 🙂