This is off wikipedia :)
"Halter" is a term used to describe a type of horse show class where horses are shown "in hand," meaning that they are led, not ridden, and are judged on their conformation and suitability as breeding stock. Depending on breed and geographic region, such events may be called Halter, In-Hand, Breeding, or Conformation classes.
An event that judges young people on their ability to groom and present a halter horse is called Halter Showmanship or Showmanship In-Hand. In most breeds, the exhibitor is given a score that breaks down to be roughly 60% on showmanship or skill, 40% on grooming and preparation, though precise standards vary by breed and discipline.
Almost every horse breed has halter classes of some type. Halter classes are usually grouped by breed, sex, or age. Rules, breed standards, clipping patterns, grooming styles, use of grooming products and popularity of the halter discipline varies widely. However, all classes require that horses be meticulously groomed before entering the ring, be trained to stand correctly in the style dictated by their breed or discipline, and to walk and trot on command in a designated pattern or line. The breed of horse in the ring can sometimes be determined by grooming style and presentation alone.
A good horse can never be a bad colour...