Cover picture: The cortical mechanisms for computing color are thought to depend on Double-Opponent cells, although the existence of these cells is debated. Here, "cone-isolating" stimuli were used to map the spatial extent of the cone inputs to four cortical color cells; the resulting maps represent the receptive field of each color cell. All the maps in one row are from the same cell: the surround response is shown first, then the center response, and finally a composite. Green indicates regions that were excited by M cones and suppressed by L cones; red indicates regions that were excited by L cones and suppressed by M cones. The surrounds show doughnuts of excitation surrounding the center responses. This "Double-Opponent" structure is critical to models of color constancy (our ability to determine the color of an object despite changing illumination conditions). For details, see the article by Conway in this issue (pages 2768-2783).