Which is NOT a factor of conformation?

Conformation refers to the physical shape and proportions of a horse, which are critical for its performance, soundness, and overall effectiveness as a working animal. The factors that contribute to conformation include breed, size, and structure, as these aspects directly influence how a horse moves and functions.

Color, however, is not considered a factor of conformation. While color may be important in certain contexts, such as breed standards or aesthetic preferences, it does not affect the horse's physical structure or its ability to perform. Therefore, color is unrelated to what is evaluated in terms of conformation, making it the correct answer in this context. Understanding that conformation primarily deals with the anatomy of the horse helps clarify why breed, size, and structure are crucial considerations in evaluating a horse's conformation.