The Austrian zoologist Karl von Frisch began the exploration of color vision in honey bees when, in 1919, he asked whether or not bees have color vision. He performed an elegant experiment that showed not only that the bees could discriminate colors but that they demonstrated associative learning. He first trained his bees to feed from a small dish filled with a nectar-like sugar water. This dish was placed on a piece of blue colored cardboard so that the color was visible to the bees as they arrived at the dish and fed. Next, von Frisch placed identically sized pieces of cardboard in varying shades of grey, each with a dish, all around the blue piece. Lacking color vision, the bees should visit one or more of the gray pieces as often as the blue piece, but he found the vast majority of the bees flew directly to the blue piece of cardboard on which they had previously obtained their reward. The bees largely ignored the gray pieces which had not been rewarded. Von Frisch repeated the experiment with other colors like violet and yellow and got the same results. Later other researchers used this experimental design to test the color vision of vertebrates.