Some musicians and composers have a brain disorder that allows them to “see” music as colors or shapes. This sensory disorder is called synesthesia. Mozart is said to have had this condition. He said that the key of D major had a warm “orangey” sound to it, while B-flat minor was blackish. A major was a rainbow of colors to him. This may explain why he wrote some of his music using different colors for different music notes, and why much of his music is in major keys.