all of those who don't think the line becomes close to invisible in deeper water should really start to reasearch red and how it appears underwater.i've red plenty of articles by divers ,scientists and photographers on the subject.the evidence is there that it does become camoflaged into it's surroundings .Water acts as a selective filter. If one were to suspend a white light above the surface of a tank of water that was 1000' deep, the colors from the white light would be filtered out selectively one-by-one. It is gradual. There is no abrupt interface. For example, most of the red is gone from the light after 10 feet. Some of the orange is gone. Less of the yellow is lost, etc. At 25' most of the orange is gone. At 35' most of the yellow is gone. This continues through the spectrum until all that is left is violet light and that fades out after hundreds of feet. So, at the bottom of this 1000' tank of water there would be little or no light!
water as you go deeper has less light and becomes murkier in all but the clearest of lakes.this causes red cast which turns greyish to blend in and be less visible.it's like when you are driving through a haze you can't see anything that's grey either.it's also the reason underwater photographers use special filters and programs to compensate for color changes in their underwater photos.