UK paramedic here, our ambulances are green and yellow purely for the purposes of visibility.
The yellow is reflective and highly visible in all conditions, the green is the necessary darker tone to pair with yellow to increase that visibility even further.
I think research has shown it’s the most visible colour pallatte for all conditions.
Our police cars are blue and yellow (the reflective patterns anyway, cars are white), same reasons, but people have always assosciated blue with the police, green with paramedics. Our uniforms are green too.
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