Pharrell is the most consistently on-record synesthete in modern music. He has described his chromesthesia in interviews across two decades: songs arrive with colors, he evaluates mixes partly by whether the colors are right, and he has said he would be lost without it, calling it his only reference for what things should sound like.
The 2008 N.E.R.D album Seeing Sounds is named for the trait, and Pharrell has discussed it in settings from music press to a university lecture circuit, including conversations with researchers. His descriptions match the clinical picture of chromesthesia: involuntary, consistent, tied to timbre and harmony.
He has also connected specific work to specific colors, describing tracks in terms of burgundy or baby blue the way another producer might name keys. Among living artists, his case is about as well documented as self-report gets.