Color constancy is the ability of the human visual system to perceive colors of objects as relatively constant under varying lighting conditions. This means that a red apple will appear red whether it is viewed in bright sunlight or under the dim light of a room. Our brains adjust for changes in light, allowing us to maintain a consistent perception of color. This phenomenon occurs because our eyes and brain work together to interpret colors based on surrounding colors and lighting. Factors like the light source, surrounding colors, and even the time of day can influence how we perceive color, but our visual system compensates to keep colors stable.