1. To change the default appointment color, first go to Account > Account Settings and select the General tab.
2. From this page, under Calendar Settings you can select an Appointment Default Color for appointments that do not have a color assigned. Select the color from the options. Or for more selection, click Web Colors and choose your color.
3. When finished, scroll down and select Update Entire Profile to save you default color.
You can always Change the Color of an individual appointment or set up colors for a specific type of appointment using Appointment Profiles.