Everything is blooming most recklessly; if it were voices instead of colors, there would be an unbelievable shrieking into the heart of the night. ~ Rainer Maria Rilke.
The beauty of spring inspired the poet to write this verse, but my neuroscientist mind reading it always thinks of Synesthesia. The word, from Greek, means “to perceive together” and refers to the experience of atypical sensory responses to stimuli. One of the most common responses is sound-color synesthesia – when you see sounds as colors. There are reports of the reverse - color evoking sound, or grapheme-color synesthesia where words or letters are associated with color, or even emotions like fear triggering visual imagery. People who experience things this way are called synesthetes. Famous synesthetes include Vincent van Gogh who associated musical notes with colors, and Vladimir Nabokov who saw letters in color.