This would benefit users. If the Event title displays as 1 color and shows the colored categories next to the title, a user can quickly see which categories the event relates to.
For example, our site has events that are for participants, some that require volunteers, some that are for the general public, and some that are all 3. The event color defaults to 1 category (which I can't determine how to control the default category), so someone might overlook that event, not realizing that it relates to more than 1 category. It's hard to explain, so I hope this makes sense! :)