Dogs and cats see the world very differently than we do as humans. Their perception, senses and color awareness is quite different from our own.
A simplified explanation is that our eyes contain cells called cones. There are three different types of cones. Cones catch light and respond to color. The more cones contained in the eye, the more colors one can see along with a greater degree of vibrancy and richness. Humans have three different types of cones and in addition, have a great number of the cones themselves. It’s the combination of these three cone types along with how many actual cones exist, that allow us to see the full spectrum of color along with a high degree of intensity.
Dogs eyes contain cones, but only two types. Where humans see the rainbow spectrum as violet, indigo, blue, green, yellow, orange and red, dogs see this same spectrum as dark blue, light blue, gray, light yellow, brownish-yellow, and dark gray. From this, we can determine that dogs basically perceive the world in variations of blue, yellow and gray with no green to be enjoyed.
Cats eyes are believed to contain three types of cones like humans, but they are not believed to have as many cones as we do. This results in them seeing colors such purple, blue, green and yellow but colors of red and orange are most likely viewed as shades of gray and they do not see vibrant colors as we do.