Ewald Hering is renowned for his work in studying the psychological aspects of color perception. In the late 1800s, he developed the theory that the human eye and brain are responsible for the perception of color. This theory has since become known as the Hering Theory of Color Vision.

Hering was among the first to suggest the presence of three types of color receptors in the human eye. Two of these receptors, called cones, are responsible for perceiving color. The third receptor, called a rod, is responsible for perceiving light and dark. Hering theorized that the cones were responsible for perceiving primary colors (red, green, and blue) and that these three primary colors could be combined to create all other colors.

Hering also determined that light from the world outside the eye is necessary for seeing color. He hypothesized that, when there is not enough light, the rods will detect light and dark but will not be able to detect color. Thus, he concluded that color vision is based on the comparison between the light from the world and the light detected by the eye.

Moreover, Hering suggested that there may be a fourth receptor responsible for perceiving color, called a “purple cone”. This suggestion was based on light experiments, in which subjects were exposed to different wavelengths of light and were then asked to identify the colors they saw. However, the existence of a purple cone has not yet been confirmed.

Hering’s insights into the mystery of color perception continue to be widely accepted and have been the catalyst for further development and research in this area. His work on the human eye and its relation to color vision has been integral in understanding the science of color perception.