Found it:roflThere was another thread that covered this topic. I shall see if I can dig it out for you:thumbsup
Thats what Ive been told elsewhere too mate, and its handy on long cold drives to keep you awake allegedly. I still think its pretty pointless myself, but hey ho :hihiI have them on Mine...mine has the electronic (Buttons) Heater controls
The centre vent has a Roller type control in the middle with blue and red dots on it.
If i want hot air out of the centre vent it i move it so i can see 2 or 3 red dots and if i want cooler air i move the control to show blue dots.
this works even if i have Hot air blowing out of the screen and or footwell vents.
so i guess it's so you can have cooler air blowing onto your face and still have warm air onto your feet or screen to keep you comfy.
Hope this helps,