Which color horse is characterized as a blue roan?

A blue roan horse is specifically characterized by a coat that consists of a mix of black and white hairs, giving it a bluish appearance. The key feature of a blue roan is that the base color is black, which results in a dark coat interspersed with white hairs. This combination creates the illusion of a blue hue when viewed from a distance.

Other colors described in the options do not fit the definition of a blue roan. For instance, while a grey horse may have a coat that includes white hairs, it does not have the characteristic dark base associated with blue roans. Similarly, a dark blue horse does not exist within standard horse color terminology, and while a red horse mixed with white hairs could produce a palomino or chestnut-like appearance, it does not align with the definition of a roan. Thus, the blue roan is distinctly identified by its mixture of black and white hairs, making the correct identification clear.