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Normal human eyes include three-colour detection cones. When comparing how the incoming light activates these cones, our brains differentiate between red wavelengths from green and blue wavelengths from yellow. Like most other animals, a dog's eyes have just two types of cones. This allows your brains to differentiate between blue and yellow but not red and green.

Jay Neitz, a colour vision scientist from the University of Washington who has performed numerous modern colour perception experiments in dogs, states that the eyes of our pets are similarly structured to those of red-green colour-blind people, whose eyes also lack that third type of cone usually present on humans.

We can acquire an idea of what dogs sense, said Neitz, if we take their brains to interpret impulses from their cone cells like the colour-blind brains.


O perceive blue and yellow, dogs and people depend on neurons in the retina of the eye. These neurons are activated due to the yellow light found in cone cells (also in the retina), but when blue light touches the cones, the activity of the neurons is reduced. The dog's brain interprets the excitement or inhibition of these neurons alternately as the feeling of yellow and blue. However, red light and green light have a neutral impact on the neurons in dogs and colour-blind people. The brains of the dogs do not detect any colour, with no signal to interpret these colours. They perceive shades of grey where you see red or green.

"The feelings of red and green would be absent from a person," Neitz told Life's Little Mysteries.
"But whether or not the feelings of the dog are lacking red and green or the brains assign other colors, is not clear."


Furthermore, dogs may utilize different signals like colour-blind humans to discriminate between the colour that we name "red" and the colour we call "green."

"There are excellent hints to assist kids figure it out many times; red things, for instance, tend to be darker than green ones," Neitz added. "So, if it is a black apple, a Red Green Color Blind man would know he is probably a Red Apple and it may be a Granny Smith if this is a lighter apple."