Each calendar entry shows user abbreviations in the top left corner of the entry. The abbreviations for the creator of the entry and the users invited/taking part of the entry are shown.
The breakdown of abbreviations:
The first abbreviation: The creator of the entry
The abbreviation in light grey: The user has not reacted to the invite (approved/declined)
The abbreviation is stroke through: The user has declined the invite
NB! Once an invite is accepted, the entry turns into the colour set for the user who accepted it. The user who sent out the invite is always the one whose abbreviation is show first.