Horses have limited color vision compared to humans, but they do not see in black and white. Horses have dichromatic vision, meaning that they are able to distinguish two basic colors and all combinations thereof along with black and white.
The two basic colors that horses can see are blue and yellow, and their color vision is comparable to that of a human with red/green color blindness. Horses are able to distinguish green from gray about as well as they can distinguish blue or yellow from gray, but behavioral studies indicate that it is difficult for horses to distinguish red from gray. Horses can see red, but they are not very good at discriminating between different kinds of red to the extent that they can for other hues.