The point is that the Royalty 'is' a commercial fishery that sells day tickets and not just for RDAA members.
Bona fidi ticket holders also walk the banks skylining the swims and is no different.
In my opinion, skylining doesn't make a lot of difference here as it is a commercial fishery where the fish see anglers on the bank every day of the week and have done so for ever. In my experience, the wearing of brilliant white or highly coloured clothing does not make any difference to catches or even spook fish on this fishery! The fish are aware that anglers are on the bank and they always have done and are well accustomed to it. They may be cautious at times but not always as you can see from the consistant catches and re-captures that take place throughout the season. In fact, in my 'past' experience, skylining actually can encourage fish into a swim where the fish then expect bait to be put in when they show themselves to be present!
I think Nigel's point is more relevent to Health and Safety and Insurance implications for non ticket holders on private property, which I think makes more sense. There is also the problem of ticket holders not wishing to be disturbed when staking fish or relaxing, by other ticket/non ticket holders walking the banks wishing to talk and gain information.
Basically, it is a commercial fishery so you would expect this.