A blue vest, bandana, or leash can look official, but blue does not have one universal meaning. Some handlers use it to mark a working dog. Others use it because they like the color. You cannot read a job title off fabric alone. What you can do is treat an unfamiliar dog as if it might be busy, and wait for the person holding the leash to decide whether contact is welcome.

Service dogs are trained to help a specific person with a disability. They may guide someone with limited vision, brace a handler who needs mobility support, or alert to a medical change. When that work is happening, blue gear is sometimes a quiet sign that the dog should not be called, fed, or petted. A moment of attention from a stranger can break a task the handler depends on.

Therapy dogs do different work. They visit hospitals, nursing homes, schools, and similar places to offer calm company. Blue can also appear on puppies and dogs still in training, closer to a student-driver sign than a finished credential. Those animals are learning public manners. Crowding them makes the lesson harder. None of this turns every blue collar into proof. Plenty of pets wear blue for no reason except that it matches a coat.

Other colors and tags exist, and they vary from one owner to the next. The useful habit is simpler than decoding gear. Give space. If a dog looks focused, stay back unless the handler invites you in. The next blue vest you see might belong to a service dog, a therapy visitor, a trainee, or a pet whose person likes the color. Courtesy works in all four cases.