[header] How to use color when fly fishing [title] Know how fishes' eyes are structured. [step] Human retinas contain two kinds of receptor cells, rods, and cones. Rods enable us to distinguish light from darkness and to see at lower levels of light, while cones function in brighter light and enable us to see colors. 
Fish eyes also contain both rods and cones, allowing them to see in color, with the proportion of rods to cones dependent on whether the fish inhabits relatively shallow or deep water. [title] Understand how water depth affects light penetration.