The simple fact is fish eyes see better underwater than human eyes. They are some of the oldest eyes on the planet as eyes evolved under water and had to adapt above water. That said brains have come a long way, too (though it doesn't feel that way most of the time). They are certainly seeing the line but what they interpret that as is another question. We throw some of the weirdest things in the water and they try and eat them...a buzzbait?! When you're not at the top of the food chain, things can be food or you can be so being alert/skittish can save your life. So, in my mind, the line isn't natural to their world and it matters or it doesn't. I love dragging a tube..a tube does not look like a crawfish and it doesn't look like a baitfish. A goby - ehhhh..kind of? Who KNOWS what they interpret that as, but they eat that on the regular. All that to say - they're seeing fluoro, braid, and mono. Use what you want and you'll catch some of the fish all of the time, none of the fish some of the time, but you'll never catch all of the fish all of the time.