Did you noticed if any of the rain gear was on sale?
Are you familiar with the term "Refractive Index".
Fluorocarbon must have a very similar Refractive Index than that of the water and thus will appear to become invisible to the human eye when put into water.
Different fishing lines have different optical properties and therefore different Refractive Indexes.
We see things in the water when they have a different refractive index than that of the water. The greater the difference in the Refractive indexes the easier it is to see.