Event categories can be retrieved from lookup or choice fields. In choice fields you enter possible values in the column settings. In lookup field you define a second list and manage your lookup values there.

• Create a new list for event categories.
• Use the “Title” column for the category name (you can also define a new column with another name).
• Add new column to set the color for each category.
  • The color field can be empty.
  • The color may be entered as color name (e.g., red).
  • The color may be entered as hexadecimal number (e.g., #FF0000).
• In the calendar events list, add new lookup column for category pointing to the Categories list.
• In the web part settings, set “Allow Categories”.
• In “Category Column Name”, select the lookup column you’ve just created.
• In “Color Column Name”, select the color column from the Event Categories list.