We use yellow for our space awareness products as it is the official warning colour for caution. A pure yellow is the most luminous of all the colours of the spectrum so the human eye processes yellow first. It's the colour that captures our attention more than any other colour so it can be seen from a distance.
Why do we not use neon yellow?
Neon yellow is primarily a colour from the green colour family. It is a mixture of yellow and green colour.
Yellow also represents cowardice, sickness, and jealousy.
Yellow is a hazard.
And that is why we are the "yellow army".