It is a myth that trout are colorblind. In fact, many shallow water fish of both oceanic and fresh water systems such as the trout or salmon have well defined color vision and can even see colors that we humans are not capable of seeing. The trout’s vision traits evolved as it did in other animals as a mechanism to allow them to better separate potential food items from the background. For example, in a watery habitat the background may be located at the bottom of the water which is normally a tarnished olive to green color or the background could even be the water itself. When looking horizontally through clear water, the background appears to the trout as a pale, silvery blue color. This phenomenon is known as background space light and is caused by the scattering of blue light as it passes through the water. In water with a lot of suspended algae, the background space light is typically found to be a greenish yellow color whereas in bog water, the background space is more likely to appear a reddish brown color.
One of the reasons many fishermen use flies or lures with strong coloration is to make them stand out more against the background space light and attract fish. The red and yellow fish lures and flies are quite popular among many fishermen today for this reason. Fluorescent colors are also quite popular as they stand out stronger than most lures and flies and have highly fluorescent shades that are very attractive to salmon and trout in the area making them much more likely to bite.
Trout can distinguish colors with ease and do not usually discriminate between very fine shades of any color for selective feeding purposes, rather they may discriminate between four or five shades of color varying from the palest shade to the darkest when feeding. The reason for their lack of color hyper-sensitivity is that since their food organisms vary slightly in color, if the trout were too sensitive to color much of the food would get away.
Interestingly enough, It has also been found that those shades of color consisting of more chroma ( meaning it appears to be more intense than the color of the natural) are more attractive to selective trout. Along with being able to better find food this way, the fact that trout see further into the ultraviolet range than humans do (they see colors that are not visible to us), could be another reason for why they are more attracted to the colors with more chroma. This also means that the watery environment the trout reside in could be influencing the transmission of specific colors. In addition to this, skylight varies during the day. In morning and evening it contains more red resulting in reds, oranges and browns standing out more during this time.
The rods and cones in a trout’s eyes physically swap places at both the start and end of daylight. In the evening, the cones which give rise to color response but need high light levels to operate are withdrawn into the surface of the retina and the rods obtrude. At dawn this action is reversed. How the trout’s brain assesses the combined cone response and what the fish experiences as a result of this response is still something that scientists are trying to figure out. However, it is definitely clear that fish such as the trout possess the mechanism for full color vision as we humans know it, and with somewhat a higher range than what we can even comprehend.