Several applications allow to share resources among users on the same system, e.g. shared calendars, task lists or notepads. Users can assign categories to items inside these shared lists, e.g. events, tasks or notes. Additionally, users can assign colors to these categories.
Opposed to the shared lists, items, and categories, these colors are not shared. Instead, each user can define his own colors, according to their personal preference. One reason for this is, that people might already use the same color for a personal category that another user assigned to a category of a shared item.
Administrators can define a default set of categories and colors for all users of a Horde system though.