It was long speculated that dogs were completely colour blind, seeing the world in black and white. In recent years, studies have confirmed that dogs, although not able to see the full colour spectrum as humans, can see limited colour because they have a red-green colour deficiency known as Protanopia. 1% of human males also have this phenomenon. With Protanopia, the eye lacks the long-wavelength sensitive retinal cones making it impossible to differentiate between the green-yellow-red section of the colour spectrum.
For the protanope, the brightness of red, orange, and yellow is much reduced compared to normal. This dimming can be so pronounced that reds may be confused with black or dark gray, and red traffic lights may appear to be extinguished. They may learn to distinguish reds from yellows and from greens primarily on the basis of their apparent brightness or lightness, not on any perceptible hue difference. – from Wikipedia
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Liz Bradley is a dog lover who lives in Ottawa, Ontario with her husband,