A small sample of a color. Paint stores, for example, have color swatches that are small squares of paper in the colors they offer so you can bring them home and see how they look in the room you're painting before making a purchase. In this case, it's a fake nail in the color of the polish so you can see what your hand would look like with a nail that color before buying it.

A color sample, usually for paint or fabric. Those cards at the hardware store with all the paint colors, the books at the carpet store with all the samples of color and texture options, online fabric stores will send you collections of swatches before you buy yardage.