In many calendar software there is an option to have different events highlighted by different colours. I know for example that many of my colleagues use different colours to distinguish meetings related to different clients or projects with different colours.
I have survived this far by just having all the events in single colour. I've only used different colours to separate whole different calendars from each other as I usually have several open in the same view.
But as my meeting count has drastically gone up during the past year it's starting to get difficult to get a good overview of my days just by glancing at the calendar. It just seems like it's all meetings.
Unlike my colleagues I can't really use different colours with different projects or customers as I'm involved in way too many. There isn't enough reasonably distinguishable colours to make that work and having close enough colours with different things would just make things confusing.
After a careful consideration I came to the conclusion that the type of the event and what kind of participants there will be are the most important things I want to see when looking at the calendar.