Do vowels have colors? According to some with synesthesia, yes.

It’s hard to pinpoint when synesthesia, the rare neurological condition where a stimulus that affects one sense prompts a response in a different sense, was first documented. Scientific literature marks its beginning in 1812, when it appeared as an aside in a Bavarian medical student’s dissertation. Toward the end, there’s a small section where he detailed how he associated musical tones and letters with colors.