Dog Colour

Dogs are often said to see in black and white, but their eyes contain two kinds of colour-sensitive cone.^{1, 2}

People have three, so a dog sees colour, but a narrower range of it.^{1, 2}

The modern evidence goes back to 1989, when J. Neitz, T. Geist and G. H. Jacobs tested three dogs in a series of behavioural experiments.¹ They measured the dogs' sensitivity to light across the spectrum and ran direct colour-matching tests.¹ The results showed two classes of cone pigment, one peaking at about 429 nanometres and the other at about 555.¹ The authors concluded that dogs have dichromatic colour vision.¹

In practice, a dog's colours run along a single axis from blue to yellow.² Light at around 475 to 485 nanometres, which a person sees as green or pale blue, looks white or grey to a dog.² Colours that people see as green, orange and red are hard for a dog to tell apart.² A dog's retina also has only 10 to 20 per cent of the cones a human retina has, so colours may look less intense.²

Whether dogs actually use the colour they have was tested in 2013 by Anna Kasparson, Jason Badridze and Vadim Maximov.³ They trained eight dogs outdoors to pick one of two paper squares, where the rewarded square differed from the other in both colour and brightness, dark yellow against light blue or dark blue against light yellow.³ In test trials the two cues were set against each other.³ The dogs chose by colour rather than by brightness, even though the brightness difference was large enough for them to use.³ The authors concluded that colour may be a basic part of how dogs perceive objects.³ The belief that dogs see no colour has outlasted the evidence against it.²

What dogs see is a world with fewer distinctions in it, sorted more by blue and yellow than by red and green.