The outer ring displays hours and the inner ring minutes
Choose colors either with the color picker or by entering a hexadecimal code
Hex codes start with "#", contain 0-9 and a-f, and are six digits long. If your code isn't valid, the color will not change!
If you do not want to select a minute-ring color, the minute ring defaults to 50% the luminosity of the hour ring
Tap the screen to switch between minimal rings and a stats page with:
steps, heart rate, calories, battery charge remaining, date, distance, active zone minutes, and elevation gain (in floors)
No free version, currently
To access the settings page in the Fitbit app, click on your device on the "Account" page. Choose "Clock Faces", select this clock face, and select "Settings" on the bottom. These are screen shots of the paid version's settings.
If you toggle between text input and color selector, it will display the last color you entered
Double check that any text hex code starts with a "#"