A fish's ability to see line depends on a variety of factors.
It's a question that's perhaps as old as fishing itself. Can fish actually see the line underwater?
FIX has constructed some interesting infographics that may change the way you think about fishing lines. It turns out the answer to the age-old question whether fish can see your line is more complex than one might first think. It depends on many factors, including the depth you're fishing, water clarity and the type and color of line you're using.
Source: Fix.com Blog
It shouldn't be too surprising that clear monofilament is one of the most versatile lines you can use if you're looking for something that'll be near-invisible to fish in most situations. And it's also not too surprising that Fix.com names heavy braided lines as being one of the most visible. A heavy braided line is the strongest stuff you can buy, but is likely not the best choice for heavily pressured and easily spooked fish!
In the end, it all comes down to the type of situation you are encountering while fishing. Some colored monofilaments, such as yellow or green are going to work better in muddy or green-hued water. Some colors, such as red, become darker and more visible at certain depths while others, like blue may become more invisible on par with clear monofilament.
But if you're really looking for the ultimate in invisible lines, it seems fluorocarbon is the way to go due to its excellent light refraction properties. And pink fluorocarbon may be even better due to the fact the color pink is less visible at depth.
So there you have it, yes, fish will see your line depending on the depth you're fishing and what color you're using. I guess you can never have too many rods and reels rigged up for anything you might encounter. Keeping these variables in mind may help you boat more fish this season.