I suppose it's all about contrast in different light conditions. But are we talking about visibility from the air, or visibility on the ground?

You don't see a lot of orange/pink fire trucks. But yellow seems to be more common than red. Yellow trucks stick out in the dark. Must be some science behind that.

The cops on foot, plucking speeders out of multi-lane traffic are in yellow jackets. They stick out like a sore thumb. They also have a lot more guts than I do. Yikes.

And then there's a totally different angle: consider the colours that will get you "found" on the ground when SAR is looking for you, and you are immobile.

The blaze orange and neon yellow still stick out, even in fall leaves. But they also make your fellow hikers' eyeballs bleed, and offend the aesthetic of the landscape, so nobody wears that stuff. But I find that anything in a light-to-medium blue, on the ground, catches my eye instantly. A knife or axe with a blue splotch of paint is instantly found; so is a fragment of those horrible blue plastic tarps. It's totally out of place.

This has me rethinking my blend-into-the-landscape solo walking gear.