Animal color vision
Short answer
Horses are not fully color blind, but they are dichromats with two cone types. They see blues and yellows well and cannot separate red from green, like a person with red-green color blindness.
In detail
Electroretinogram flicker photometry on domestic horses found exactly two cone types, with peak sensitivities near 428 nm (blue) and 539 nm (yellow-green). That two-cone retina is why horses separate blue from yellow well but see red, orange and green as variations of one muted hue.
In a plate test built for human color deficiency, horses failed every red-green plate and passed the blue-yellow plate. That is why traditional orange jump markers give little contrast for a horse, and why yellow, blue and white stand out more.
Horses carry 2 cone classes to our three. The missing long-wavelength class is what turns red, orange and green into one axis for the animal.
| Cone class | Horse | Human |
|---|---|---|
| S (blue cone) | ~428 nm | Nearest: S cone ~420 nm |
| M/L (single long cone) | ~539 nm | Nearest: M cone ~530 nm |
Horses see a blue-yellow world. Electroretinogram flicker photometry on domestic horses found two cone types, one peaking at about 428 nm in the blue and one at about 539 nm in the yellow-green, with no third class for the red end of the spectrum. Two cone types give dichromatic color vision: blues and yellows are vivid and distinct, while red, orange, yellow-green and green all fall along a single dimension the horse cannot break apart.
Behavioral tests agree with the physiology. In a two-choice task using pseudoisochromatic plates of the kind used to screen children, four horses passed the gray demonstration plates and the tritan (blue-yellow) plate, but none could read the protan, deutan or combined red-green plates. The authors concluded horses are dichromats whose color vision resembles that of humans with red-green color deficiency. Earlier discrimination experiments had already shown horses separating blue and yellow from gray more reliably than red or green.
Color is only one part of equine vision, and not the part the eye is optimized for. Horses have the largest eyes of any land mammal, a horizontal pupil, a reflective tapetum behind the retina, and a rod-dominated retina — all adaptations for spotting movement across a wide, flat horizon at dawn, dusk and night. The eyes sit on the sides of the head, giving a field of view of roughly 350 degrees with a narrow blind zone directly in front of the nose and another directly behind.
This is the trade-off most grazing mammals made. Sensitivity in dim light and coverage of the horizon mattered more to survival than telling red from green, and two cone types were enough for the visual tasks that remained: finding water, reading the sky, and noticing a shape that moves against the grass.
A 2020 study from the University of Exeter modeled the color and luminance contrast of the traditional orange markers used on fences and hurdles at eleven UK racecourses. For horse vision, orange had poor visibility and low contrast against most surroundings, while yellow, blue and white were more conspicuous, with the exact ranking depending on the vegetation behind the fence. When racehorses were then jumped over fences with orange, fluorescent yellow, bright blue or white takeoff boards, fence color changed both the angle and the distance of the jump.
The practical lesson generalizes beyond racing. Anything meant to be seen by a horse — a pole, a gate, a fence line — should be chosen for contrast in a blue-yellow world, not for how bright it looks to a trichromatic human. Orange is the classic mistake: it is highly visible to us and nearly invisible to them.
The mechanism is genuinely similar. A human with protanopia works from an S cone and an M cone, with no L cone; a horse works from an S cone and a single long-wavelength cone at about 539 nm, which sits closer to the human M cone than the human L cone. Both lose the same red-green axis, which is why the palette above is rendered with the protan simulation. The difference is that in a horse this is the adapted normal state, not a deficiency, and the rest of its eye is built around it.
If you are curious how your own color vision compares, the free screening on this site estimates whether you have a red-green deficiency and which type. Most people who take it see all six swatches as different colors; a protan or deutan viewer sees something much closer to the horse's column.
The horse's column above is close to what a person with red-green color blindness sees. The free color blind test takes about two minutes and estimates whether you have a red-green deficiency and which type.
Screening only — results estimate color vision on an uncalibrated screen and are not a diagnosis.
Animal color vision
The full comparison table: dogs, cats, birds, fish and the mantis shrimp by cone count.
Are deer color blind?
Another dichromatic grazer, and why blaze orange is safe to wear.
Are dogs color blind?
The best-studied dichromat, and why a red ball vanishes on green grass.
Color blindness simulator
Run your own photo through the same Machado model used on this page.
Last reviewed September 12, 2026. Cone peak values are from electroretinogram or microspectrophotometry studies of the species named; behavioral claims are from the cited discrimination experiments. Simulations approximate the color differences lost, not the animal's experience.