Probably one of the most frequently asked questions about a dog is whether they can see in colour.
We now know that dogs can see in colour, but just not the same way people with normal colour vision do. The number and vibrancy of the colours they see are limited compared to ours.
The eyes of both people and dogs contain special light catching cells called cones that respond to colour. Dogs have fewer cones than humans, this suggests that their colour vision won't be as rich or intense as ours. However, the trick to seeing colour is not just having cones, but having several different types of cones, each tuned to different wavelengths of light. Humans have three different kinds of cones and the combined activity of these gives humans their full range of colour vision.
The combined activity of the red, green and blue cones is what gives people their full range of colour vision. In contrast, canine eyes possess only two types of cones, those that detect blue and yellow. Scientists believe the colour vision of dogs is roughly like the vision of people with red-green colour-blindness since they, too, only have cones with two photopigments. So, while people with full colour vision see a rainbow of colours — red, orange, yellow, green, blue and violet — dogs see greyish brown, dark yellow, light yellow, greyish yellow, light blue and dark blue.
One funny odd fact is that the most popular colours for dog toys are red or safety orange. However red is difficult for dogs to see. It may appear as a very dark brownish grey or perhaps even a black. This means that bright red dog toys are visible to us may often be difficult for your dog to see.
So now you know why your dog may have more fun chasing after a bright yellow tennis ball on green grass under blue skies but have trouble finding the red ball. The yellow ball is simply easier for your dog to see!