The order in which your employees are displayed in the calendar corresponds exactly to their order in the "Staff" app. You can find it in the main menu under Set up your company.
If you adjust the order here, these changes become visible right away in the calendar.
Hint: To change the order, click on the three horizontal grey lines to the left of the employee you want to move, hold down the mouse button and drag to desired position.
Please note: If you have several branches, you first need to select a branch in the employee list.