When you see a dog out in public, it’s natural to want to greet or pet them. But before you approach, it’s important to pay attention to what the dog is wearing.

Many dog owners and handlers use colored vests, leashes, or bandanas as a way to communicate important messages about their dog’s needs or behavior. One color you might notice is blue—and it carries a very specific meaning.

1. Blue Often Represents a Service or Therapy Dog

In many countries, dogs wearing a blue vest, leash, or harness are typically service dogs. These dogs are highly trained to assist people with disabilities, whether visible or invisible. Their tasks can include guiding the visually impaired, alerting a person with epilepsy before a seizure, providing mobility support, or calming someone with PTSD.