By default when an appointment is added to the system it will appear red in the Day Planner calendar.
This means that the customer has not confirmed that the appointment is ready to go ahead.
In order to confirm an appointment simply edit the appointment to be confirmed and then click on the confirmed checkbox.
Click on the Save button to update the appointment in the database and the appointment will now appear as green in the Day Planner calendar.
For further information, please watch this video