Cam/tone-down was in my office during my last MoD tour, and even had the pleasure of discussing aircraft cam with Mr [Grey] Barley.
You can’t hide, but you can confuse, CF-18 cockpit painted on the underside, for example, although the airframe favours that. We discussed large contrasting areas of colour, a bit like the WW2 black/white undersides, and how extending that idea could actually confuse in a close visual engagement. You can rarely optimise cam for every environment/background, so confuse instead.
As for airfield cam ... loads of radar reflectors, including ‘false positive’ IPs, is a fairly cheap option. And fill the ‘black hole’ of the airfield’s radar/IR signature ... again cheap and easy. At high speed, low level, it doesn’t take a lot to confuse or throw off aim in a SAM-intense environment (if we had one).