Think of the last dog you saw. Now, think of the collar it was wearing. If you are like most people, you probably have no idea if there was a design on it or if it was a solid color, but it turns out that sometimes what a dog is wearing is incredibly important - especially if it is red.

A red collar, bandana or even a red leash could be a pet owner's way of warning those around them. So what does it mean? Well most people know to associate the color red with "stop," and that's just what it means when a dog has it on. Veterinarian Dr. Brian Evans told Reader's Digest, "Red is the signal that this pet is aggressive and needs space from both people and other animals. These are pets that have been known to snap or bite at passersby, attack other dogs, or lunge at people. These pets may be perfectly fine at home with their owner but become overly protective of them when they are out."

This might come as a surprise to many people, even to dog owners, but using colors on pups as a way to communicate to others has been going on for some time in professional settings. The National Association of Canine Scent Work is a big fan of it, with one animal behavior consultant explaining, "The red bandana simply warns others to give the dog distance, yet allows the person and dog to participate in relative safety."

So what do you do if you see a dog in red? Well it doesn't always mean to stay away, but regardless of what color a pooch has on, you should always ask the owner permission to pet their dog.

There are other colors to be aware of too. Yellow means that pets can be nervous and, because of that, unpredictable. Like a traffic light, it means that you should slow down and be cautious around them, but there is no need to outright stop. Also like a traffic light, green means that the dog is approachable, but you should still ask for permission from their owner. Orange signifies that a dog doesn't interact well with other animals, and blue typically means that the pooch is a working dog, service animal or in training and shouldn't be touched for those reasons.