I guess black is as good a colour as any other for high visibility but it's just the latest fashion in a long line of colour schemes that come and go. Obviously, there is no ideal colour scheme, so it'd just a case of whatever the right people think is "cool" at the time. Hopefully, the fashion will die before too long and we can look at something a little more attractive. I mean, black Dominies? Eugh!
Anyway, Jet Provosts should be grey with dayglow stripes - that's what a "proper" JP should look like!