tuxfoo: thank you for the pointer to GetAllCalendarsFeed(): I kinda overlooked that possibility.

Upon inspection of CCalendar API, it's possible to flag a N900 calendar as read-only, so that should do the trick. I just have to figure out how to get the same information from Google Calendars, but I suspect that it won't be too difficult.

Concerning the colours, unfortunately the N900 palette of colours available to the calendar is quite limited (ten colours or so), whereas Google's palette is a bit more extended, so it won't always be possible to have a 1:1 matching between the two.