Eric
I think you'll find the orange immersion suits are that colour so they are visible in the sea, but I agree with you viz a viz the fluoro jackets.
There will be a rule somewhere that says they have to be worn (because we have to be seen to be doing everything reasonably practicable to protect personnel, including personal protective equipment such as these) without anyone with more than one brain cell doing an assessment on what the actual hazard is and the best way to mitigate it.
As has been mentioned before, now we all have to wear them they lose their effectiveness. What you need to do is come up with new and constructive methods to make sure you are seen, and change them over regularly so that they don't get tired and worn out. The old hunter instinct means that your eye are attracted to movement (such as the prey running away from you) but when you are the one moving in a vehicle you don't get the same effect