Scientists have long known that dogs' eyes are physically equipped to perceive colors, and consequently that canines are not colorblind. But dogs are believed to see only shades of yellow, blue, and gray. That's because their eyes have only two types of color-sensitive "cone" cells as compared to three in the human eye.

Given their limited color "rainbow," do dogs really make use of their color vision to make decisions – or do they depend solely on levels of brightness?

"In the past, it's been easier to test whether dogs respond to brightness," says Dr. Stanley Coren, a University of British Columbia dog vision expert who was not involved in the new research. "But testing whether they use color discriminations is so much more difficult. So it hasn't been clear whether, at a conscious level, dogs are using color."

To get a better picture of dog vision, researchers at the Russian Academy of Sciences in Moscow tested eight untrained dogs using pairs of contrasting colors on paper squares – dark yellow with light blue or light yellow with dark blue. The squares were placed in front of boxes containing meat, one of which was unlocked. Then, through a series of 90 trials for each dog, the animals were trained to associate a certain color with the unlocked box and, consequently, the meat reward.

Next, the researchers removed the color that the dogs had been taught to associate with the meat reward, and presented just two choices to the dogs. If a dog had been taught to look for dark yellow to yield a reward, for instance, it was offered only light yellow and dark blue to choose from. This way, the scientists could tell whether the dogs were using color or brightness to make their choice.

So how well could the pooches use color to choose the right box? More than 70% of the time, the dogs correctly picked the box displaying the same color, and a whopping six out of the eight dogs went for it 90 or 100% of the time – indicating that the dogs were making decisions based on the color of the square alone, not its degree of brightness.

"The dogs could, in fact, switch over and make the proper color distinction," Dr. Coren said. "It proves that not only do dogs have color vision, but they also consciously use it."