key
the whole point of the red key is to allow people to add and remove keys from the immobliser i.e. if you lost the blue key, you would use the red key to delete that key from memory so it any wannabe thief had your key, they wouldnt be able to start the car.
The red key also allow's additional keys to be added to the system and is also used to allow another copy of a blue key (i think, bearing in mind i dont have any of this key crap on my car)
Also i think people needs to get some facts straight instead of posting thoughts i.e. illegal to sell the car without a red key, or use it to start the car every 3-6 months.