Unless the event is at night, and headlights (whether human or machine mounted) are being used, there's no point in having retroreflective strips. The idea of these is that they reflect light almost exactly back to where it came from so they show up very well if you're wearing a head-torch or driving a car with headlights, but not at all if it's a daytime event.
Blue and ultraviolet light have no brightness (if you're ever in a club, look (briefly) at an ultraviolet strip light. It will have colour (deep blue) but little or no brightness). It's impossible to make a bright blue jacket, which is why there aren't any. High-vis jackets are typically fluorescent - i.e. they take in blue light and let it out at lower frequencies in the spectrum e.g. red, yellow or green. This means that they can be brighter than a white surface, and the colours draw attention to the vests.
I can explain chromaticity co-ordinates, but they're unlikely to be useful unless you have access to a spectrophotometer or at the very least a chromameter and calibrated light source. As an aside, the most commonly used chromaticity co-ordinates were developed by the physicist Schrodinger. They're very counter-intuitive in part for the joy of it, and in part because they were designed around a mechanical calculator that couldn't deal with negative numbers. I can also discuss the neurophysiology and evolutionary reasons as to why blue has no brightness (unless you're a dolphin).*
Checking the British Standard or using hats sounds the best idea to me. I'm interested to hear that you're only meant to wear orange if you work on the railways, which I didn't know. I bought a few yellow fluorescent mesh jackets from Ebay and they were surprisingly cheap - I think I paid about £2 each. It's important not to wash them too often as the dyes wash out or are broken down quite easily.
*I spent several years sitting through presentations about what colours different fire-extinguishers should be in Australia, and how many colours there are in Russian versus Hungarian rainbows. This hasn't proved very useful to me in later life, so forgive me for showing off when the opportunity arises.