Edward's inherited synesthesia was consistent and stable throughout his lifetime. His took a standard form: seeing numbers as colors.
Baudelaire and Rimbaud wrote poems about synesthesia. Kandinsky wrote about it and perhaps used it in his art. By the middle of the twentieth century, synesthesia was still present, of course--Nabokov was describing his colored graphemes and putting them to dazzling use in his anagrammatic wordplay.