Although an early and influential review led to the often-cited conclusion that color vision is rare among mammals, more recent findings suggest that it is actually widespread. According to Jacobs (1993, 2004), all non-nocturnal mammalian species that have been adequately examined show some color vision capacity, although the degree varies enormously. Data on the presence and characteristics of color vision in the horse, however, remain sparse (and almost none in the case of ponies). Eight Caspian pony (four mares and four stallions) were presented with a series of two-choice color vs. grey discrimination problems. Experiments were performed in a box of 3 x 3 meter containing a wall with two translucent panels that were illuminated from behind by light projected through color or grey filters to provide the discriminative stimuli. Ponies were first adopted to the stall (box) with two panels in it and then learned to push one of the panels in order to receive the food rewards behind the positive stimuli in an achromatic light-dark discrimination task, and were then tested on their ability to discriminate between grey and four individual color: red (617 nm.), yellow (581 nm.), green (538 nm.) and blue (470 nm.). The criterion for learning was set at 85% correct response, and final testing for all color vs. grey discrimination involved grey of varying intensities, making brightness an irrelevant cue. All ponies were tested with all four colors vs. grey discriminations. Except 2 of animals, the rest of the ponies successfully reached the criterion for learning blue color vs. grey discrimination. Only 2 ponies reached the criterion for learning green color vs. grey discrimination. Except 2 ponies none of the ponies reached the criterion for discriminating red and yellow vs. grey (respectively). The conclusion is that ponies can discriminate between the four selected color vs. grey.

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