Harbisson was born with achromatopsia, a rare disorder where one is completely color blind. This isn’t red-green blindness, which occurs much more commonly in populations. Harbisson sees the world entirely in grey.
However, working with a cyberneticist, Harbisson helped to design an antenna-like “eye” that plugs into the back of his head. The eye senses colors, then converts the light frequencies into sound frequencies, which Harbisson perceives through bone conduction. He can, quite literally, hear color.