You can color code the events on your calendar using a category field in your app. You will find this option in the dropdown menu next to any category field in your app's template.
When you've enabled the "Color in calendar" setting, the event will use the color for the selected category when displaying items in your calendar. This coloring will apply to all calendar events related to that item, so if you have multiple date fields in your app the color will show the same for each entry.
Only one category field can be used to set the color for your events. As shown in the screenshot above, a small calendar icon will appear to the left of the category field that is being used to color your events.
Pro tip: If you would prefer that all items from a certain app show in the same color rather than separating them by a category, you can add a category field to your app and add a single category option. If you mark that field as required and enable the "Color in calendar" option, then all created items will have that category, and thus will appear with that color on your calendar.