Four students in my course presented their group project on synesthesia and language today. Very little is really known about synesthesia, though some interesting research is being conducted now. Many famous writers, among them Baudelaire and, most famously, Nabokov, were synesthetes as well.
As I listened to my students, though, my thoughts turned to children's writers--especially those who write alphabet books. Do they associate color or personality to a grapheme or phoneme? Obviously if you are writing an aiplane alphabet book, for example, content is more important than color or sound. But if you're writing Chicka Chicka Boom Boom (Bill Martin Jr.) or Dr. Seuss' ABC: An Amazing Alphabet Book! maybe content is less important than how mischevious certain letters are.