Job: To guide their visually impaired or blind handler.
Handler: May or may not show signs of visible disability.
Gear: Visual Assistance Dogs will wear a guide dog harness, typically of which at least some part is white. White is the color protected for use by guide dogs and visually impaired individuals.
Notes: Visual Assistance Dogs are commonly called “Guide Dogs” or “Leader Dogs.” Most are Labrador Retrievers, Goldens or German Shepherds, but they can be any sturdy, even-tempered, medium or large breed dog.
excerpt taken from http://www.anythingpawsable.com/types-of-service-dogs