The Pawtrack collar has a GPS receiver built into it. 

This receiver is located on the part of the collar to go on to the back of the cat’s neck, this is to give the receiver a clear view of the sky so it can get messages from the satellites easier and hopefully obtain a more accurate GPS position.

While the Pawtrack collar is on GPS rather than WiFi the LED will be RED.

For more information on how the receiver work please have a look at "How does GPS work?".