Question:

Why should I define a colour and font style for each option?

Answer:

You can define a font style and a colour for each option. This setting is assigned to the various paragraph and character formats so that you do not need to set anything further when editing the calendar template in InDesign. These settings are optional.

Some of the options are related because they share a certain format. If you change a setting there, it will also change in the linked options.