Whiteboards display the Workout of the Day or a Lesson Plan, or something akin that needs to be put up on a TV screen.

You can now change the background color of your whiteboard by navigating to the Whiteboard in question and clicking Edit Whiteboard.

Near the bottom, click Background color.

Find your color choice and save.

You can preview the full whiteboard via this button.

Note that if a workout isn't scheduled for today, you won't see anything listed here. You can always temporarily change an upcoming workout's date to today to view it here.