Dogs can see blue and yellow, but they cannot see red or green. What we call red appears greenish to dogs, and green appears brownish-yellow. Dogs also have difficulty distinguishing between shades of blue and violet.
The world appears to dogs in shades of blue, yellow, and gray. This is a much more limited color range than what humans see, but it is still enough for dogs to get by. Dogs rely more on their sense of smell than their sense of sight to navigate the world.