Why black, blue , silver and orange are probably the best colors for trout fishing? Nobody knows exactly but lot of fishermen use these colors for making their flies. It seems that these colors are widely used in Europe, Asia, USA because they really work
For example black gives you the perfect contrast in deep water or in muddy rivers. Then silver combine with black activate the side view and side detection of the fish. Orange represent a good attractor for predators. And blue color reflect the blue light that penetrates the water and make the fly visible in deepest parts of the rivers and lakes. For those who do not know , the blue color is the light wave who penetrate the best the water column. This reason what blue lures are for deep waters and catch fish better then anything else. If you add a little bit of blue, your nymph will be better detected by the fish in deep waters even if the outside light is poor.