The keepers were surprised by this. Do elephants see in color? There was nothing in the books about color perception among elephants. Ruby also had a strong preference for certain colors: red, blue, and yellow. Were these real preferences or was Ruby merely pointing to colors at random? To find out, the helpers switched the position of the jars on the palette and offered more jars. They discovered that, regardless of position and other choices, Ruby continued to choose red, blue, and yellow most often.
The keepers also noticed that Ruby often used colors that matched objects around her--construction vehicles working nearby and even the clothes worn by visitors to the elephant barn."
--Dick George, Ruby: the Painting Pachyderm of the Phoenix Zoo (1995)