You might spend time trying to decide whether your dog prefers the red ball or the green one, but it appears your deliberations might be in vain.

That’s because scientists say your four-legged friend can’t distinguish between the two colours as they are red-green colour blind.

The condition, known as deuteranopia, is rare among humans and is said to affect 1% of the adult male population.

Dogs are crepuscular animals, meaning they are biologically designed to be more active at dawn or dusk.

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However, after becoming man’s best friend following domestication around 10,000 years ago, they now mimic human behaviour and are mostly awake during the day. But, their eyes, specifically when it comes to colour, haven’t yet evolved to suit daytime vision.

Scientists from the University of Bari in Italy used a modified version of the Ishihara’s test – a colour perception test for red-green colour deficiencies featuring circles with numbers on them.

But instead of using numbers, they used an animation of a running cat.

Results showed that most of the dogs could not see the red-green animations – suggesting they couldn’t distinguish between the colours.

A modified colour blind test was developed for dogs.
A modified colour blind test was developed for dogs (University of Bari)

The researchers wrote in their paper: “Overall, our results, together with the above-reported studies, confirm that dog colour vision is dichromatic in its nature, resembling that of human red-green blindness.

“Besides contributing to increasing knowledge about the perceptual ability of dogs, the present work showed, to our knowledge, for the first time, directly canine red-green blindness by using a modified test of colour vision in humans (Ishihara’s test), thereby allowing direct comparison to colour vision (and colour blindness) in humans.”

The research is published in the Royal Society journal Open Science.