Use a fluorocarbon line. If you are going fishing in light cover, clear water, or rocky terrain, often a fluorocarbon line is the best choice. It is much less visible than braided line, and has excellent abrasion resistance to get around rocks and logs. Fluorocarbon line is, in fact, almost invisible under water as it has a light refractive index that closely matches that of water, so the light passes through the line without reflecting back.
Use a clear line. A clear blue fluorescent line is absolutely perfect for fishing in the sunshine. Under the water it will remain clear so the fish can’t see it, but the light from above the water will reflect off of it so that you will be able to see it from above the water. You being able to see the line and keep track of it when the fish can’t is a good start.
Use a gold high-viz monofilament line when you need to see multiple lines. If you are out fishing and you have numerous lines out, it can be hard to keep track of them all, especially if the sun is reflective off the water strongly. Gold monofilament line is a good choice for these conditions, but it will be more visible to the fish than a fluorocarbon or clue blue fluorescent line.