Frisch was the second to demonstrate that honey bees had color vision, the first being Charles Henry Turner which he accomplished by using classical conditioning. He trained bees to feed on a dish of sugar water set on a colored card. He then set the colored card in the middle of a set of gray-toned cards. If the bees see the colored card as a shade of gray, then they will confuse the blue card with at least one of the gray-toned cards; bees arriving to feed will visit more than one card in the array. On the other hand, if they have color vision, then the bees visit only the blue card, as it is visually distinct from the other cards. A bee's color perception is comparable to that of humans, but with a shift away from the red toward the ultraviolet part of the spectrum. For that reason bees cannot distinguish red from black (colorless), but they can distinguish the colors white, yellow, blue and violet. Color pigments which reflect UV radiation expand the spectrum of colors which can be differentiated. For example, several blossoms which may appear to humans to be of the same yellow color will appear to bees as having different colors (multicolored patterns) because of their different proportions of ultraviolet.