For every scientist who has claimed horses are colorblind, there is a horse owner who refutes that theory with anecdotal proof; it is a much-debated question in every corner of the industry. Do horses see color? “Because of its special relationship with humans as a companion and a form of transportation, as well as a beast of burden and source of recreation, there are probably few animals that have more often been the subject of curiosity about alternate sensory worlds than the horse,” researchers wrote in the most recent study on color vision in horses. These researchers sought to clear the cobwebs shrouding this vision mystery, and in their search, they discovered horses don’t have as well-developed color perception as a normal human – but they also do not see their world in shades of gray.

The Basics of Sight

When light flows into the eye, it is focused by the lens and sent in a straight beam to the retina, a specialized tissue at the back of the eye made up of two types of photoreceptors. When the beam of light hits these photoreceptors, it is converted into electro-chemical messages, which are transmitted into the brain via the optic nerve. Color is created when the light stimulates these messages in the cones, the first type of photoreceptor and the instrument of color vision. The specific color created in the brain depends on the size of wavelength and the type of cone that accepts it. Light is separated into many different wavelengths, and each one corresponds to a different color based on its length. Shorter wavelengths stimulate blue; medium wavelengths become green, and long wavelengths register as red in the brain. Each of these wavelengths matches a specific cone in the retina; there are several types of cones, and each one has a special affinity for a specific wavelength size.

Rods are the second photoreceptor type, and they adjust sight to dim lighting or darkness. Although they are the most dominant receptor in the horse, horses also possess two classes of cones, indicating they are anatomically built for some color perception.

The most recent research indicates that horses do see colors – just not every one in the rainbow.

A Unique Color Palette

Humans with normal vision are referred to as trichromats or “three colors”; they have three types of cones, which enable them to pick up the four basic colors – blue, green, yellow and red. In contrast, horses have dichromatic (“two colors”) vision; they have only two types of cones, indicating their color perception isn’t as diverse as a human’s. To explore the difference, a group of researchers at the Medical College of Wisconsin and the University of Wisconsin-Madison tested six ponies by shining a band of color into the eye and evaluating how the cones responded to the stimulation. A thin electrode lying across the eyeball picked up the nerve signals given off by the photoreceptors and sent the readings to the computer. This method revealed the horses were sensitive to blue and green light but not to red, indicating horses have only two types of cones. The first type is sensitive to short wavelengths or blue light in an identical way to its human counterpart. The second cone type registers medium wavelengths or green light; this cone is slightly different than a human’s because the green light takes on a yellowish cast. Therefore, horses can easily see blue and greenish shades in their environment, but red appears as a brown hue with a blue/yellow tint.

Light is separated into many different wavelengths, and each corresponds to a different color in the rainbow.

A New View of the World

With this recent research, the gap between scientific evidence and the horse-owner’s proof is bridged – finally. But with the restored peace comes a new understanding of equine vision that should do more than satisfy your curiosity. The unique range of colors your horse can see should affect any visual cues you use in your training and could shed light on previously unexplained behaviors. In addition, we also understand that your horse sees a slightly blurred world, much like a near-sighted person, which means he relies on patterns of behavior and movement more than features to recognize people and objects at a distance. Although in those two capacities his vision is slightly compromised, his night vision is excellent, which stems from his well-developed rods. Knowing these three principles of equine vision should help you adjust your behavior and training methods to better fit the needs of your equine companion.