For a long time, veterinarians thought dogs could only see in black and white -- but the truth is a little more Technicolor and less "Casablanca." As University of Washington vision researcher, Jay Neitz, recently told Live Science, dogs' sense of perception is the same as the way people with red-green colorblindness can see.
To dogs, the world looks a little different -- purple is blue, green takes on a yellowish color and red becomes dark brown. (That's because dogs only have two types of color-sensing cones in their eyes, as opposed to humans' three.) But dogs can still use certain cues to tell differences in objects.
In 2013, a group of Russian researchers trained dogs to associate a color, such as dark yellow, with a reward. They then gave the dogs an option -- picking from a light yellow or dark blue square, for example. More than 70 percent of the time, the dogs picked the correct color, rather than the shade of the square.
Both color-blind humans and dogs can use color, rather than brightness, to make distinctions between objects. "A lot of the time there are good cues to help them figure it out; for example, red objects tend to be darker than green objects," Neitz said to Live Science. "So, if it's a dark apple, a red-green color-blind person would know that it's probably a red one, and if it's a lighter apple, it may be a Granny Smith."