As a general rule, bright orange is the most visible color under most conditions. Sometimes, however, the way the sunlight hits the water make it appear lighter or darker. Rather than green or blue, the water can often appear white or light gray in color. In that case, a black-tipped float is actually more visible.

One trick is to put white out on the tip of the float and just paint or use a magic marker on top of the white out to make the float tip whatever color you want. If you ever want to change the color, you can just scrape off the white out.