Josh McDermott lectures on how the visual system determines the lightness and color of surfaces, part of MIT's course 9.35, Perception, from Spring 2024. The lecture examines why the brain's estimates of surface lightness depend on context rather than raw light intensity, covering phenomena like simultaneous contrast and lightness illusions where identical patches look different depending on surroundings. McDermott extends the same logic to color, discussing how the visual system separates the color of a light source from the color of a surface it illuminates, a problem known as color constancy. The talk draws on classic psychophysical demonstrations and models of how neurons and perceptual mechanisms might solve this underdetermined inference problem, situating the material within the broader course sequence on visual perception. Runtime is 79 minutes, consistent with a full lecture rather than a condensed summary.