Multiple project support for JIRA calendars

Requested from comment in: TEAMCAL-267:

I have a customer who uses JIRA to manage professional services. This means that a single user can be involved in many projects. I have also set up confluence as their document repo, and added team calendars as well. Its a 5 user pilot currently. One thing from team calendar, which this issue appears to address, but could go a little further, is the requirement to specify a project. If we could specify a saved filter in JIRA rather than a project we could see multiple projects with a single add. Some intelligence to add different colours for all projects would be nice too