Schrödinger first proposed in the 1920s that color perception could be mapped in a three-dimensional space. He suggested that the eye’s three types of light-sensitive cells — often linked to red, green, and blue — shape how people experience hue, saturation, and lightness. His concept helped scientists think of color not just as a physical property of light, but as something organized inside the visual system.

For decades, the theory influenced research in vision science and color studies. Yet key parts of the framework were never fully defined. One major gap involved the so-called neutral axis — the range of gray shades stretching from black to white. Schrödinger referred to this axis but did not clearly define it, leaving an important question unanswered. Researchers say that this gap has now been closed.