Final answer:
The opponent-process theory of color vision, where color is coded in opponent pairs such as black-white, yellow-blue, and green-red, is best illustrated by observing a colorful sunset, as it may lead to the experience of negative afterimages and reflects dynamic changes in color perception.
Step-by-step explanation:
The opponent-process theory of color vision is best illustrated by observing a colorful sunset (option C). According to this theory, color is coded in opponent pairs: black-white, yellow-blue, and green-red. This means that within the visual system, cells are excited by one of the opponent colors and inhibited by the other, explaining why we do not see combinations like 'greenish-reds' or 'yellowish-blues'.
The experience of negative afterimages also supports the opponent-process theory. Staring at a bright-colored object and then quickly looking at a white surface can result in a perception of the complementary color, as described by the opponent colors listed above. Similarly, seeing a black-and-white photograph (option D) can be explained by this theory due to the black-white opponent process, but it doesn't demonstrate the theory as effectively as a sunset, which involves dynamic color changes and has the potential to trigger the opponent color effect.
While the trichromatic theory applies to the retina where cones respond to three different wavelengths representing red, blue, and green, the opponent-process theory applies once the signal moves past the retina to the brain. These theories are not mutually exclusive and work at different levels of the nervous system. Color perception, including both theories, is an essential function of the eye and brain's color-sensing system.