When the color of a shirt or other garment differs from the color of the body of that garment. The whole collar needs to be a different color. Do not use when only the frills on the collar are a different color. For dress shirts the collar is usually white with matching cuffs. This is then called a Winchester shirt. Sailor collars are almost always contrasting in color, thus tagging dress shirts, dresses and other garments is more useful.
