Cajun Red, Cajun Blue, Fireline, Power Pro, Spiderline, Trilene XL, Trilene XT, Stren Clear Blue, Stren Fluorescent Blue, Seaguar, Vanish, Walmart Special at 2.99 for 1000 yards, any other line you want to mention....they all work well. They all have their uses. Somewhere, somehow, someone likes one of them and hates another one of them.
As for line disappearing in water.....that's for magicians. Maybe fluorocarbon is a lot less visible in the water than the others but it does have quite a few disadvantages too. Objects reflect light. They reflect different wavelengths and according to the wavelength, we see colour. What colour do fish really see is hard to imagine. Some fish do not see some colours but they still see the object. As the object goes deeper into the water, certain wavelengths are stopped by the refraction of the water. Red is among the first colours to disappear to our eyes. However, the object remains visible. It just no longer reflects red. The red gets darker and darker as it gets deeper. The only time it really disappears is when there is no light. Everything is black. Even the colour white has turned black.
Also, think of this and picture in your mind a scene we often see on t.v. and movies.....Thousands of fish swimming in the sea. All packed together yet swimming in the sea. We see them suddenly all change directions at the same time. All changing speeds at the same time. A perfect harmony as if one solid body moving in the water. No fish bumps into another fish. How do they do this? It's not from an external signal way off to one side. It's due to the fact that fish are very sensitive to movement. Movement causes very slight changes in pressure. Just like a rapidly moving piece of cloth makes sound (a speaker). When one fish moves slightly toward it's neighbour, there is a pressure change between the 2 fish. The same when one fish moves very slightly away from it's neighbour. Eyesight also contributes to this phenomena.
Now, moving a line in the water also causes a very slight pressure change. I bet a fish can feel that pressure change, no matter what colour the line could be.