FISHING IN
COLOUR
Sunlight is made up of seven colours, red, orange, yellow, green, blue, indigo and violet (hey just like a rainbow). When light hits something it is absorbed but some, according to spectrum is reflected and we see colour. The sea filters out these individual colours in the same order, red goes first at 5-10m violet being the last to vanish. The depth at which they are filtered out depends on water clarity and light intensity, i.e.your red shock leader appears black to the fish if the water is deep enough. This also explains why many deep sea benthic organisms are red.
Anglers are presented with line, beads, attractors and lures in a wide range of colours. When spinning it is always a good idea to walk along the pier to determine what colours are working. It is often suggested on sunny days the warm colours should be used and on dull overcast days that the cold colour are better (now there's a chance for some angler to blow a £30 000 grant in the name of scientific research). This is based on the notion that fish seem attracted to red so if they can't see red then orange is the next best colour and so on. If this theory is correct then why are lures not marked with the depth at which they are most effective, this would be of great help to boat anglers if not the shoreman. The sliver shiney side of metal lures will only reflect the light available at the depth it is used, i.e. in very deep water they will appear violet. This perhaps explains why silver is a good all round colour to use.
Aquarists know that when feeding medicated food to sick fish adding a drop of red food colouring encourages fish with poor appetites to feed. In shallow water red food dye makes a good bait additive, whether or not other colours will work at greater depths is worth investigating.
Many fish are capable of changing colour by moving pigment granules around their chromatophores. fish affected by parasites or under stress will fade in colour. This is one of the tricks used by aquarists to avoid buying poor stock and to spot trouble early on. Fish use this to spot healthy mates for spawning and of course easy prey. Lures which are too vibrant may send out the message "I'm healthy, you can't catch me". But in poor light or at depth some of the warm colours on the lure will black out making it look different.
When it comes to leader line I like to use grey as I seem to catch more fish although many will argue that colour does not matter or even that some colours attract fish. There is no hard evidence either way but it is worth using red when fishing piers and harbours with deep water close in. It will appear black to the fish but will be easy to spot when it comes to the surface. Bright vibrant colours for the main line will help prevent crossovers at crowded venues.
And finally a note of amusement. Scientists working to reduce shark attacks on divers and during air/sea disasters have discovered that wearing red is not a good idea. Discussing this with a marine biologist who had worked in his native Maldives for many years he informed me that 97% of shark attacks are on white people (it's true, I've checked). Concerned that sharks may be racist I asked him if there was a scientific reason for this. He paused for a while then answered "Yes, we're not stupid enough to go in the water".