Hi support,
I have tried this in IE 7,8,9 and 10 and the problem is over all versions.
What I have done is this: I have setup a plain text attribute called "AppointmentColor" in the appointment BO with several color options (red, blue, green etc.). I have then in the calendar query item rules added the following item rule (s): " Appointment.AppointmentColor='Red' " and choosen a red color as the background color for that item rule. The result is shown below:
In Chrome:

In IE:

Thanks