EXTNAME_CATEGORIES

VEVENT CATEGORIES are stored as an extended property with this CalendarContract.ExtendedPropertiesColumns.NAME.

The CalendarContract.ExtendedPropertiesColumns.VALUE format is the same as used by the AOSP Exchange ActiveSync adapter: the category values are stored as list, separated by CATEGORIES_SEPARATOR. (If a category value contains CATEGORIES_SEPARATOR, CATEGORIES_SEPARATOR will be dropped.)

Example: Cat1\Cat2