Dogs are basically color blind. They see red and green like we see the color brown. They can differentiate between these two colors by size or brightness, but not by color. Humans have three different color cone cells in the retina, dogs only have two cells. Humans have red, green and blue cone cells and dogs only have yellow and blue. While cones in both dogs' and humans'
eyes help them to see colors, rods in both of these mammals' eyes help to detect motion.
Dogs do have more rods then humans, they can see moving objects much more clearly. Dogs vision on a daily basis have a blurred and dull image, unless the object is moving. This is why they rely on their nose more than their vision.
Dogs have something humans do not have, a tapetum lucidum. A tapedum is a reflective surface behind the retina that reflects light back through the retina, increasing the light available to the photoreceptors. Also, a dog has very large pupils that dilate more than ours, which allows more light to enter the eye. This is why a dogs eyes will shine in the dark. Cats have the same ability. This is why they can see much better in the dark, especially if the object is moving.
Different breeds of dogs see differently based on the shape of their nose. Dogs that have a long straight nose, have a wide field of excellent vision. It is more like what we see when we look through a pair of binoculars. A dog with a short nose, like a pug or bull dog, tends to see things more like a human's vision. They do not see things from as far away as a dog with a longer nose. That is why they are not as good at hunting and do not chase things as much as other dogs with a longer nose.
There is an application on the internet that allows you to see what your dogs sees, called Dog Vision - very enlightening.
Last bit of information is that when a dog is born, the first thing that opens for their use is their nose, then the ears and finally their eyes. This is also the order in which a dog will use their senses on a daily basis.