How Horses and Humans See Color

Source: Paul/Flickr

Sitting on a horse, it’s easy to assume that she sees the same view we see. But she doesn’t. Riding is a team sport in which two partners experience the world simultaneously but in very different ways. Color vision is a great example.

Human color vision improved through evolution by the recruitment of brain cells from centers responsible for the sense of smell. This theft, so to speak, gave us the ability to see about a million different hues as we gaze around our environments. It also left us with a pathetic disability in detecting odors. Compared to other mammals, color-centric humans can hardly smell a thing.

By contrast, the equine brain has all the neural machinery to detect and follow scents as well as a bloodhound does. To give you an idea of what that means, a bloodhound can locate a scent 12 days old from 12 miles away, and then track it for 130 miles. Horses have a terrific sense of smell…but the ability to detect only about 10,000 different colors. And most of those colors are faded.

So what colors do horses see? The strongest shade is yellow. Just ask the folks who posted a big bright yellow “Yellowstone” sign on one end of a performance arena in 2021. Their effort to honor the creator of the popular television show caused 19 young horses, all finalists for the championship title, to refuse to gallop toward the sign. Printed in any other color, most of those horses wouldn’t even have noticed it.

Red and green are indistinguishable to horses—so a red jump on green grass, for example, is hard for a horse to see. This fact caused every steeplechase hurdle in the United Kingdom to be altered beginning in March of 2023. For decades, bright reddish-orange poles marked these hurdles, which are leaped at high speed. When equine color research was publicized, racing authorities realized their horses couldn’t even see those poles against the green grass. The color is now being changed to white in an effort to reduce horse and rider injuries.

One of my favorite questions on this topic is “How do we know?” Horses can’t tell us which colors they do or do not see, which are bright or faded, or which don’t contrast against a background color. The answer is that we seek converging evidence from comparative anatomy and behavioral training studies.

The anatomy of a horse’s retina does not include the types of cells that allow humans to distinguish between red and green. This was a big clue to the hypothesis that perhaps horses could not tell those colors apart. So experiments were devised in which horses were trained to respond (by pushing a lever, for example) to differences in color.

Once a horse is trained to respond to color variation, experimenters can display a wide range of hues to them. If the horse can see a difference between red and green, for example, he will push the lever in hopes of receiving a reward. But if red and green look the same to a horse, he will not push the lever because he can’t detect the difference between the two colors. They are the same to him.

Next time you watch a horse-and-human team compete—in a race or jumping competition, perhaps—marvel at the wonder of what you are observing. Prey and predator mammals working together in precise cooperation and extreme athleticism despite enormous sensory differences in their experience of the world. What an amazing partnership.