Which horse color has a body resembling a "smoky or mouse-colored" appearance?

The correct answer is Grullo. This color is characterized by a unique appearance that can be described as "smoky" or "mouse-colored," resulting from a specific genetic combination. Grullo horses typically have a coat that is a diluted black or gray, often appearing as a grayish-brown color. The presence of a dorsal stripe and other primitive markings can add to their distinct look.

Understanding horse colors involves recognizing how genetics influences the physical traits of a horse, including coat color and patterns. Grullo stands out due to its specific dilution gene affecting black pigment, creating the desired smoky appearance. This is in contrast to the other colors listed, each of which has its own distinct characteristics and coloration not matching the description given.