Regarding the use of strobe lights, you are required to have a flashing light active while airside, no matter if it is blue or yellow. So they would activate blue ones when responding, letting both aircraft and vehicles know that they are "in a hurry". When patrolling/returning etc. they would use yellow lights, helping aircrafts localize them, but still letting other vehicles know that they don't need to overtake them. They probably don't want to use both of the lights, hence it might be irritating, drawing to much attention, worrying passengers, etc. Summing up, they don't have to use both. Let me know if I can help with anything, I am into aviation. And I am looking forward to this mod!