When you are editing within a single calendar day box, you cannot assign font colors or styles to the text.

However, both Repeating Events and Calendar Overlays allow you to assign colors to the events or overlays. Therefore, you can use events and overlays to cause certain text to have whatever color you like.

Here's an example using overlays. Let's say you are using the main calendar (calendar 1 in your account) for a public camp schedule, and you'd like to have camp dances appear in pink, and camp concerts in blue:

1. Turn on multiple calendars, e.g., so you can use calendar2 for camp dances & calendar3 for camp concerts
   
2. You should now see a '2' tab for calendar 2, and a '3' tab for calendar 3
3. Click on the '2' tab. You are now viewing calendar 2. Enter in all your camp dances. Click on the blue bar's 'customize' command fill in the name field with 'Camp Dances', click on update).
4. Repeat step 3 for the '3' tab, naming and filling in the camp concerts calendar.
   
5. Go to your calendar1 (your main calendar). Use calendar overlays to add calendar2 and calendar3. In the process of adding them as overlays you can choose colors for these overlays.

Another example would be to use repeating events to set up every birthday, and always choose magenta color for these birthdays. You could set up your car pool schedule using repeating events and color code them red.

(search terms: calendar color; calendar font color; adding color; colored text; change calendar font)