This depends which QWP version and SharePoint version the user is on.
In SP20010 starting from QWP 5.4.1, events belonging to the same calendar are automatically colored the same. Adding a new calendar will have its events shown in a new color not yet used by the calendars already added to qCalendarView. You can define your own color appearances (if you don't like the default colors) under Legend Appearance in ezEdit.
If you don't have this feature available, then you can define a new column in a calendar list that stores the name of the calendar, and configure Color Appearances based on the value of this column.