At the University of Rochester researchers have found that our perception of color is controlled much more by our brains than by our eyes. The number of color-sensitive cones in the human retina differs from person to person, but we all perceive colors in the same way. A laser-based system was used to map out the topography of the inner eye. Imaging the living retina allowed light to shine directly into the eye to see what wavelengths each cone reflects and absorbs, and which color each is responsive. Each subject was asked to tune the color of a disk of light to produce a pure yellow light that was neither reddish yellow nor greenish yellow. Everyone selected nearly the same wavelength of yellow, showing a consensus over what color they perceived yellow to be. Once researchers looked into their eyes, they were surprised to see that the number of long and middle wavelength cones (the cones that detect red, green, and yellow) were sometimes scattered throughout the retina, or weren’t present at all.