I did a paper way back in college about trout vision.. I don't recall all the details, it was a long time ago, but it goes beyond what colors penetrate water in IR/UV, etc, and right to biology of a trout.
The rods in the eye detect black and white, while cones detect color. We actually have 3 different types of cones, one of each sensitive to wavelengths corresponding to red, green, and blue. The 3 primary colors of light!
We tend to think of animals as either colorblind or color sensitive. But animals which see colors don't do so the same that we do. Depending on the cones in their eyes, they may have different primary colors than humans do. And there doesn't have to be 3, there can be 1 or 7 primary colors!
Trout it turns out have 4 cones. They are weaker than we are at discerning shades of green, and stronger at shades of red, especially what we would say is a dark, blood red is very bright to them. They also see UV, which we cannot.
With weak in green, strong in red, whats half way between? Yellow! greens look more yellowish to them, yellows look more red. Does that mean they like yellow? Have to ask a trout to know that.