Google Calendar still doesn't offer sustain for labels, but you can now pick a color for each event. By default, each event inherits the calendar's color, but you can change it by clicking the happening and using the small drop-down displayed next to the event's title.
"Color Coded Events lets you allocate specific colors to sure events: put pink on your daughter's soccer practice or make your lunch dates red. It's a great way to stay prepared, keep track of returning events, and add a little flair to your calendar. Color coding is private to you and anybody who can edit your calendar," explains Google.
If you want even more options, go to Google Calendar Labs and enable "Event flair" to be able to add icons to your events.