I once asked this question to guido hibdon a well known bass pro known for sight fishing in clear water. His response was I don’t want to spook the fish. My next question to him was why do fish swim into gill nets then. All he could do was smile and shrug his shoulders. I have fished many tournaments and spent a lot of time on the water fishing all types of fish and the only time I have noticed a difference is when I have fished heavily pressured fish and it didn’t make that big of a difference on the color of the line.