Hello,

On the appointment rectangle, the Subject property is presented. We do not provide a feature to change it to present the Description property. You can check the Description that is related to an appointment, by hovering mouse.

And for the background color of a specific appointment, you can do so by changing BackColor property of the Appointment object.

private void button1_Click(object sender, EventArgs e)
{
    this.ultraCalendarInfo1.Appointments[0].Appearance.BackColor = Color.Red;
}

If you have any question with this, please let me know.

Thanks,
Yuki