Dogs have shown a preference for the color yellow.

Dogs possess only two types of cone photoreceptors, unlike humans who have three. As a result, their vision differs from that of humans, although our four-legged friends perceive colors in their own way. Previous studies have indicated that dogs can distinguish between blue and yellow, but other colors—green, orange, and red—appear to them as muted shades of gray or yellow.

Researchers have previously conducted experiments related to color perception in dogs, but typically, subjects were trained beforehand before performing tasks. It remained unclear whether color stimuli affect untrained dogs, and if so, how. A group of biologists from the Indian Institute of Science Education and Research (IISER) in Kolkata took on this question. They shared their findings in an article published in the journal Animal Cognition.

In new experiments conducted in urban, suburban, and rural areas near Kolkata, over 450 stray dogs that roamed freely in the region were involved. Residents often feed the dogs by leaving bowls of food on the streets. The researchers utilized this common practice to observe the dogs' reactions to bowls of three different colors: gold-yellow, deep blue, and gray.

Each dog was allowed to participate in the tests only once to prevent them from memorizing the conditions. The bowls were cleaned each time to eliminate the scents of other dogs. In the first series of tests, the dogs were given the opportunity to choose one of three ceramic bowls of food, which were placed randomly on the ground at a short distance from each other.

The biologists observed the dogs and recorded the events on video. The bowl chosen was the one the dog approached first to sniff. Ultimately, 72 out of 134 dogs preferred the yellow bowls with food. Researchers observed a similar result when they repeated the experiment with empty bowls.

In the second series of tests, dogs chose between two bowls of food—blue and gray. No clear preferences were identified in this case. In the third experiment, yellow and blue bowls were used, which were covered to obscure their color. Under these conditions, the choice of bowls became random, leading biologists to conclude that the animals were indeed relying on color.

In the fourth series of tests, dogs were first given the option to choose between two yellow bowls with food and one without, and then between an empty yellow bowl and a gray bowl with food. The second bowl contained two different treats: cookies, which were also used in other tests, or a small piece of raw chicken.

When faced with two yellow bowls, dogs preferred the one containing food. In the second scenario, dogs more frequently chose the empty yellow bowl, even if the gray bowl contained more appealing food—raw meat.

The scientists proposed several hypotheses that could explain the dogs' preference for yellow. For instance, this color might be associated with food for Indian dogs, as locals often season their meals with turmeric and pepper. Spices color the food, giving it a yellow tint in the dogs' vision. Additionally, since dogs have limited color perception, raw meat and blood might also appear yellowish to them. It is also possible that vibrant yellow stands out more starkly against other colored objects for dogs.

However, the biologists acknowledged that the proposed hypotheses do not fully explain the clear preference for yellow observed in the experiments. Further research is needed to completely understand the underlying reasons.