Sound waves are a vibration (disturbance of air) that travels through a medium (air, water, a solid, etc.). The vibrations are different in size and shape, which is what produces different sounds. Sound waves can not exist in a vacuum (because inside there is no air to vibrate) but lightwaves can exist in a vacuum. Light is a wave of vibrating electric and magnetic fields. Both sound waves and lightwaves have the same shape for the most part. They are very similar forms of moving energy.
Synesthesia is a sensory disease in which “stimulation of one sensory or cognitive pathway leads to automatic, involuntary experiences in a second sensory or cognitive pathway.” Some synthesthetes associate colors with numbers, but another type of synesthesia is one in which sound is highly associated with different colors. Many master musicians have synesthesia when it comes to sound, and understand sound as a color. It helps them learn and makes them fascinated in the music. I wonder if synesthetes are somehow sensing something about the wave formation similarity between lightwaves and sound waves. It does not seem shocking to me that people associate sound and color in this way because of their similarity.
The experience of synesthesia is unique and hard for people without to understand. But similarly people with synesthesia have trouble understanding what it is like to not have synesthesia. Famous Hungarian conductor and piano virtuouso, Franz Listz, notoriously demanded to his orchestra: “O please, gentlemen, a little bluer, if you please! This tone type requires it!” and “That is a deep violet, please, depend on it! Not so rose!” Many synesthetes are highly successful creative people because of their cognitive differences.
http://www.classicfm.com/discover/music/synesthesia-gallery/#P5AXSIqw3yw6yIXK.99
I hadn’t heard that story about Franz Listz! It must have been difficult for the non-synesthetes in his orchestra to keep up. I wonder if Listz ever composed music based on a painting or other work of art. I recently saw a poster for a showing of artworks that different artists had made in response to each other (a musician wrote a composition in reaction to a painting, which was painted in reaction to a dance, which was choreographed in reaction to a poem, and so on).