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.
Another composer who had color-hearing was the Russian composer Alexander Scriabin. In 1907, he talked with another famous composer, Nikolai Rimsky-Korsakov, who had synesthesia, and they both found that some musical notes made them think of certain colors. Scriabin worked with a man named Alexander Mozer who made a color organ.
The perceptions of a person with synesthesia aren’t always a direct trading of two senses. Many also associate colors with letters and numbers, insisting that the number 7 is green or that the letter P is a yellowish orange. Entire words will have a unique color based on the colors of their component letters. This isn’t a matter of simply associating a letter or number with a color; they will actually see the colors when presented with text or even when thinking of letters and numbers.
Singer,songwriter and composer Billy Joel claimed that,
Certain lyrics in some songs I’ve written, I have to follow a vowel color. A strong vowel ending, like an A or an E or an I, I associate with a very blue or a very vivid green…I think reds I associate more with consonants, a T or a P or an S. It’s a harder sound. These [letters] are what I associate with reds and oranges.
For synesthetes, the stimulation of one sense causes the automatic stimulation of another, resulting in the ability to taste shapes, see music, and countless other variations. One synesthete may perceive each letter of the alphabet as a different color; another may have entirely separate smells for each year in the calendar.
The phenomenon–its name derives from the Greek, meaning “to perceive together”. The condition is not well known, in part because many synesthetes fear ridicule for their unusual ability. Often, people with synesthesia describe having been driven to silence after being derided in childhood for describing sensory connections that they had not realized were atypical.
For scientists, synesthesia presents an intriguing problem. Studies have confirmed that the phenomenon is biological, automatic and apparently unlearned, distinct from both hallucination and metaphor. The condition runs in families and is more common among women than men, researchers now know. But until recently, researchers could only speculate about the causes of synesthesia.
Research suggests that about one in 2,000 people are synesthetes, and some experts suspect that as many as one in 300 people have some variation of the condition.
Wikipedia has a list of famous people with synesthesia.
Source: American Psychological Association.