The use of these brightly coloured mainlines started on the Big Game fishing boats so that the Skippers could see where the various lines were in the water with the fast moving tropical fish screaming line from the reels.
Then the coloured lines became popular with our beach anglers for basically the same reason, so that crossed lines could be clearly seen at distance.

Visibility in the water is then the main reason why these brightly coloured lines have persisted with both shore and boat anglers. Make no mistake they are here to stay.

Beach anglers often fish the coloured line right up to the end rig and more than a few of them like to use the coloured line for trace lengths as well. Call me old fashioned if you like but my preference is for clear monofilament or fluorocarbon for hook lengths - but the facts speak for themselves, they still catch fish whatever the trace colour. Perhaps the fish are more colour blind than we think.

I like to use the brightly coloured braid lines for my boat fishing but knot on a thirty foot length of clear monofilament to the end rig. This is for several reasons. The first is to act as something of a shock absorber because the braid lines do not have very much stretch and some stretch is desirable although in my view the least the better. Secondly the mono acts as a sacrificial rubbing strip, protecting the braid line from the abrasion which inevitably occurs around rocks and reefs. My belief is that the braid line is not so abrasion resistant as monofilament.

The monofilament shock leader also allows rapid rig changes because familiar knots such as the blood and uni knots can be tied almost by reflex action by most anglers.