You can tap on one of the arrows and set it as "favourite" to follow it. The colour of the arrow will then change to yellow. This feature can be helpful to highlight a colleague you are flying with for example or if you plan to fly in close formation. Notice that you won't receive collision warning from aircrafts that are marked as favourites.
TCAS Mode
The Traffic awareness is set by default in the Nearby mode. You can change it to the TCAS mode by going to "Map Options - Traffic Awareness".
The TCAS mode uses the same algorithm as the TCAS present in airplanes. It will not issue a Resolution Advisory though.
