I even have to carry two different colours, as some countries require
orange, while others require the green/ yellow that we use here.

Network Rail use orange. They don't like non-railway people to wear it
on the track

Yes as drivers they say are "tuned" to see Orange and reject anything else.

You shouldn't be on the track unless you are clad in the correct attire;!.

I think you might have meant on or "about" the track?..

I've seen them use Blue in France not the most striking colour for such
applications;!..
--
Tony Sayer