Kyra Sundance, author of The Dog Rules: 14 Secrets to developing the dog you want (2009), mentions in her book that dogs aren’t color blind, they’re “color-limited” because dogs can’t see all the colors like we do.
According to Sundance, dogs see red, yellow, blue, indigo, and violet. She also states orange, yellow, and green look the same to a dog.
Though their night vision is far better than humans, it is a dog’s sense of smell which helps them determine who or what is familiar. Sundance explains that this “scent memory” lasts a lifetime and affects everything the dog does.
So if you’re taking that pooch for a long walk, let them smell their surroundings. Dogs are like computers, inputting and storing data for later use in their scent files, retrieving information to determine safety, comfort, and a myriad of things we probably haven't pinpointed yet.
That’s why it’s also important to leave a piece of your clothing when you send your pet to a boarding kennel, or leave at the vet. I’ve actually tried this. I left one of my shirts with my pet when I went on a three-day trip. My sister, who babysat, said it helped him sleep because he wouldn’t sleep until she placed it on his bed! I called him Linus for a while =)
p.s. Linus is the character from Peanuts who carries his blanket almost everywhere with him