I had the pleasure of interviewing Mr P Barley just after Gulf War I.
Things I remember (though it was a long time ago!):
1. Barley grey was all about contrast against the sky - beyond a few kms, colour becomes irrelevant to visual detection.
2. Countershading was tried - lighter undersides/darker on top - like the early Eurofighter prototypes (DA2 etc.). This again was to reduce contrast. Mr Barley delighted in telling me about how he had pioneered this in the UK using an Airfix 1:24 scale Harrier GR1 plastic kit stuck on top of what was then the Institute of Aviation Medicine near the old ETPS. I saw the pictures - true story!
3. Contrast is also the reason hawks are black - when compared against e.g. high vis SAR helo yellow, black is actually much easier to see with the Mk1 eyeball at several km ranges. So the hawks ditched the red/white and went black for safety (anti-collision, hence anti-camo) reasons. I think there were discussions about painting the sea kings black for the same reason.
4. Hemp Nimrods replaced the comically obvious gloss white roofs that were visible for miles when they were parked on the pan.
5. Psuedo "False canopies" went on the Jags for GWI - he was proud of that. I think they just painted the nose gear door black.
6. Trials were done on active light based camo on 1/4 scale tornados (ex spin tunnel models I think). Film was quite good.
Nice chap. Interesting time to be at Farnborough!