Sorry to drag you all off topic here -
Something mentioned about 10 pages back - in regards to avoiding indigo lights on vehicles, reminded me of some research I did a litttlw while back.
Vicroads regulation specifically prohibits Indigo/purple/magenta lights on your vehicle.
A lesser known fact: - vicroads patrol vehicles use flashing indigo lights.
I have verified this in person on several occasions, as they tend to use them most commonly around weighbridges
Usually when forming highway checkpoints to perform spot check on trucks/trailers etc.
This was what caused me to follow up on the regulations.
It strangely was not something I could find written in my old L or P plate books, or on my driving test, but that was a few years ago.
It would also seem that the NSW RTA, and heavy vehicle escorts also use these colours too.
Here's a link for the curious:
https://en.wikipedia.org/wiki/Emergency_vehicle_lighting