That is funny Rob, "Is a red snapper invisible?". Maybe the Cajun line disapears because mono is somewhat transparent in nature and with the line being red it is more invisible than the more common colors of mono. Maybe it's just a gimmic to sell more line?? I have no idea but you do bring up some valid questions....

Why haven't shad and other bait fish adapted and become red.

What does a trout with a nice red gill plate and a red stripe look like to a bass?

Bass must find and eat most crawdads by vibrations because they could surely never see the red ones...