The hi-vis line allows us to closely monitor the sink rate of the lure and to track what is going on very precisely. When you’re fishing a 1/16 oz. head in 10″ of water you don’t “feel” the jig hit bottom, you see it when the line hesitates and bows slightly when the jig sets down.
Contridiction? I don’t think so. Fishing line is super fine… 0.008 of an inch in diameter in the case of the 6 # line that I use… when used in moving, slightly stained or cloudy water, I think assuming a walleye will be spooked or put off by a tinted thread in the water is actually quite a stretch.
And yes, jig head color can be enormously important sometimes as is the color of plastics / hair used. Dustin and I go to the extreme of sorting extra light or extra dark ringies or k-grubs from the 100 ct. bags we get and noticing that some days the fish will show a preference for one over the other. But that’s off subject.