Cover legend: The top is an original receptive-field drawing taken from the notebooks of Hubel and Wiesel, December 11, 1962. It is the first documentation of a color-opponent neuron in macaque striate cortex. The neuron was suppressed by red in the receptive-field center, excited by red in the receptive-field surround, and excited by blue throughout. The bottom shows the response maps to cone-isolating stimuli of a similar neuron recorded in alert macaque. In the L map, blue shows regions suppressed by red cones, and red shows regions excited by red cones. In the S map, blue shows regions excited by blue cones. Like most blue-ON cells, spatial opponency was found in only one cone system (L), a feature called ³/₄ opponency. Spatial and cone opponency is thought to be important for color-contrast calculations. For more information, see the article by Conway and Livingstone in this issue (pages 10826–10846). Drawing reproduced with permission of D. Hubel and T. Wiesel.