Camouflage
In most situations, a fisherman wants his line to be as invisible to the fish as possible. If the water is clear, clear fishing line is usually the best choice, but in murky water, a clear filament may actually be somewhat visible to fish. Many fishermen prefer transparent blue or transparent green lines for darker waters.
Blacklight Fishing
For night fishing, a visible line can actually be an advantage. Blacklight fishers employ a fluorescent line and an ultraviolet light to increase line visibility. With the light, they can watch their fishing line for signs of a bite and gauge the lengths of their casts without drawing a lot of attention and spooking the fish the way a bright white line would.
Gel-Spun Polyethylene
In many cases, color is not the most important feature of a fishing line. Gel-spun polyethylene, for example, has a dark gray color that some anglers see as a drawback but is popular for other reasons. The line is very strong and has very little stretch, so many people see the color as only a minor factor. This line is particular popular for deep-sea fishing, where the color will be less visible and the strength and lack of stretch will make more difference.
