Dogs are red-green colorblind. They have only two cones in their retinas, allowing them to see yellows and blues. To a dog, orange, red and green all appear to be the same brownish-yellow color. Dogs can perceive blue colors very well.
This information should be considered when selecting toys, training aids and even dog owner clothing for optimal dog performance. For example, a bright orange ball may be visible to a human, but it looks like grass to a dog. This suggests that a better color choice for dog toys is blue or purple and white. Agility handlers should consider wearing blue shirts to allow their body cues to be more visible to the dog.