As FED says, one odd coloured blade will stand out like the dogs proverbials whereas evenly spaced bands of colour are not so obvious. The flicker effect will attract attention even when one is not looking directly at the rotors.
Moorabbin Airport has a 700’ Helicopter circuit height vs 1,000’ for fixed wing following a mid air many, many years ago when a FW let down onto a helicopter in identical conditions to all these fatal accidents being discussed. The problem is by no means a new one and ‘corporate knowledge ‘ often diminishes and has to be re-learned.