Water, lighting, and movement all affect how easily a swimmer can be seen. Colors that look nice on land can quickly disappear once they’re underwater or viewed from a distance.
Blues, greys, greens, and darker tones often blend into the color of pools, lakes, and oceans. In natural water especially, reflections and shadows can make these colors almost invisible.
Bright colors, on the other hand, create contrast. Neon orange, bright pink, yellow, and bold patterns stand out against both water and pool bottoms. That contrast makes it easier for adults supervising the water to quickly locate a child.
In crowded swimming areas where there are lots of splashes and movement, that visibility becomes even more important.