Capta, the structure was there, but in many instances, most folks never know what to look for. For example, Mahi, or dolphinfish, are quite frequently found lurking beneath small patches of Sargasso weed, or any other floating debris. Something as simple as a floating sheet of newspaper proves to be a great place to find mahi.
Bluefin and yellowfin tuna both follow specific migratory routes, which do not vary more than a few miles east or west throughout their lives. Yellowfin prefer the canyon edges, which is also the favorite haunt of marlin and wahoo. Bluefin tuna travel close to shore, often spending time foraging for small mackerel species over underwater humps and lumps. You can find some great charts of these migratory routes on various fisheries sites.
As for fish being colorblind, yes, that is true, however, they can readily discern various hues such as florescent reds, yellows, greens, etc..., colors that rarely occur naturally in nature. Thus, lures of those colors tend to be more productive because they contrast sharply with the natural environment. If course, the best lures usually have some contrasting silver on them as well. But there are other factors involved - mainly sound.
Many species, such as tuna, mackerel, bluefish, striped bass and wahoo, forage relatively close to the surface, often driving schools of baitfish to the surface and ripping through them at their leisure. One of the most exciting things anyone will ever witness is the carnage that takes place when a school of big, slammer bluefish herds a school of Atlantic menhaden into a tight ball then begins ripping through them. If the schools are relatively large, the noise is unbelievable, sounding like the roar of the surf along the California coast. When this is taking place, any surface plug, particularly silver, or blue/silver combinations, tossed into the melee is akin to rolling a wine bottle though a jail cell. It draws dozens of instant strikes the resemble a small explosion on the water's surface.
When fish are actively feeding on the surface, this is not a place for trolling. Trolling usually results in causing the fish to sound and if you are lucky you may catch one, but more than likely you will not. Under these conditions, a good spinning or bait casting outfit works best, merely by moving the boat to within about 50 feet of the fish, then casting into the melee. I've encountered large schools of breaking bluefish and striped bass mixed, both foraging on Atlantic menhaden at the time, and I just hove to and began casting, while slowly drifting along side of the schools. It has always been quite productive and you could easily fill the freezer with fresh fillets.
Many pelagic fish utilize sound to find their prey. Because of this, offshore anglers frequently employ the use of a teaser, which is a monster size lure with no hooks, but makes an incredible disturbance as it's dragged through the water in front of the lures. The fish are attracted from great depths to the teaser, then discover easy pickings on the smaller lures behind the teaser. It is very effective for marlin, giant bluefin tuna, wahoo, and big eye tuna.
The zaniest thing I've used to catch fish was small strips of red rag attached to size 1 wide gap hooks and fished on a top and bottom rig in the lower Florida Keys. This produced a solid strike as soon as the sinker hit the bottom, mainly from flannel mouth grunt, small grouper and porgie. After putting a few fish in the cooler chest, the cloth strips were dredged through the fish slime, which made it even more productive. That bright red color was something that was not natural to this environment, which in turn, got the undivided attention of every fish in the immediate vicinity.
The grunts averaged about 10 to 12 inches in length, they were easily filleted, skinned, and the fillets were then rinsed in fresh water, patted dry, dipped in a mixture of egg and milk, then coated with homemade cracker crumbs and pan fried. Oh my!
All the best,