Ok
From what I have discovered so far its not colour that results in high visibility its contrast relative to the background...hence why the zebra stripes worked so well...so it seems the key is to clash with your surroundings...incorporating a recognised pattern enhances the effect by making it register in the brain longer...
One personal take on this is HiViz clothing. Nowadays the high street is overwhelmed by Fluoro yellows and neon orange, space-lemon and retina searing lime. Everybody in a risk-assessed job or activity appears to have to wear it. Crossing patrols wardens, street sweepers, police, paramedics, crocodiles of school kids, breakdown truck drivers, window cleaners, the list is endless. Te danger then is that HiViz actually makes you blend into the background.
Psychologically speaking HiViz appears now not only to be the norm, but I also believe triggers an anonymity of the wearer. Yu see someone in HiViz and you see the clothing, and immediately associate it with a job or position of authority. You then link that with the task, not the person, so the wearer becomes depersonalised. Consider then the reaction to cyclists. The HiViz helmeted cyclist is seen as a cyclist ; the sort of person demonised by click-bait journalists, and as they appear to be equipped and shielded from harm, drivers possibly take less care. If on the other hand you were to see the nice lady from the village post office sailing serenely by in a summer dress with her hair flowing in the breeze, you are more likely to associate her with who she is, not what she's doing. Statistically no more vulnerable than the weekend warrior or MAMIL, she becomes, or remains a person the eyes of the driver, and is potentially afforded more care or consideration.
I suppose then a stand-out bike draws attention. A left-field colour scheme and way-out appearance creates a personality that may or may not bleed into the image of the person riding it. That purple hardtail with green tyres says far more about the rider than your run of the mill black framed hybrid, and so the association with a fellow human being is reinforced.