Anybody requiring driving on an airfield must be CP3 minimum (requires a "lantern test" at the Med Centre) or CP2 SAFE.
The reasons being, the traffic lights on the airfield are low level lights (red & green side-by-side), and the fact that ATC or Runway Caravan can transmit 1 light at you.
If you can't tell red/green/white apart, you would be a danger on the airfield as you could enter an active runway!!
Within the last 2 weeks, I have personally refused an airfield user permit F600A to a contractor who was as colour-blind as a bat (at his own admission and confirmed by an Ishihara Test (coloured numbers and dots and lines))
All TG9 are required to be CP2 SAFE and I believe all Flt Ops Branch should also be CP2 as they have a remit to be Incident Commander/SLOps/Wg Cdr Ops as part of their career progression.