I know that when I'm riding in a group of more than 3 no-one can hear my stock B12, which can be dangerous if I'm trying to pass someone. One of the other guys had a ZX12 and had the same problem, until he put on an aftermarket end can
Mick, the problem isn't that your bike is too quiet, it's your squidly riding buddies aren't bothering to look in the mirrors before they make a move!
(If you're talking about bikes you're passing not being able to hear you...)
As far as day glo colors, certain colors are more noticeable.
The bottom line is, it doesn't matter WHAT we do, some jerk will always turn in front of us, or pull out in front of us, and say 'I didn't see him."
I think there's a combination of 'that vehicle isn't big enough to hurt me', 'It's a bike, it can squirm around me', 'He's a dumbass to be riding a bike, and deserves whatever happens!' and people just driving with piss poor habits.
Just notice how many people never even bother to stop at stop signs, run red lights, don't use turn signals, tailgate, etc.
The bottom line is, most people can go a life time with bad driving habits, and really suffer no consequences. A minor accident involving two cars isn't a big deal. Nobody dies. If one of the vehicles is a bike, shite kind of magnifies. (And the perp usually still gets away with it...)