system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5: What makes hi-vis colors... hi-vis? What is it about hunter orange and highlighter yellow that makes them "pop" like they're glowing?
gpt
This is because they glow.

Conventional pigments reflect some colours of light and not others. For example a yellow pigment reflects yellow light but doesn't reflect blue light.

Hi viz colours reflect some light for example yellow. However they also contain fluorescent materials which glow when energised by blue or ultraviolet light.

The natural blue light in sunlight as well as UV light cause the material to actually glow, as well as being coloured.