Sony Ericsson P800 - Manual (Page 110)

110 Calendar
This is the Internet version of the user’s guide. © Print only for private use.
Entries in a folder with a specific colour appear in that colour in
Day and Week views (but not in Month view) so that you can
see the pattern of events in your diary. Reminders appear as
whatever the folder colour.
Saving changes
If you leave Calendar while editing an entry, your changes will
be saved automatically.