A lot of people assume that horses, like dogs, are color blind.
This is not true. Horses do, in fact, see color. They do not, however, see color as well as we do.
Horses have, in fact, dichromatic vision - they see the world the same way as a human male with red-green color blindness. They have particular difficulty distinguishing between yellows and greens - but they see various shades of green very well.
This all makes sense for a herbivore who needs to be able to quickly identify various plants.
The tradition of painting show jumping fences bright colors is actually to make sure the horse can see them. "Natural" obstacles are more challenging to horses.
More on equine vision tomorrow.