Lorde described her synesthesia in detail around the making of Melodrama (2017): the album had colors, violets and blues and the bruised palette of its artwork, and she has said production decisions were steered by whether sounds matched the colors she experienced. In interviews from that period she walked through how changing a sound changed its color, and how the record’s visual identity followed the synesthetic one.
Her producer Jack Antonoff has corroborated the working method in his own interviews, describing her directing sessions in color terms.
Her case sits firmly in the self-described tier: consistent accounts across many interviews, specific examples, and a documented influence on finished work. It is also a clean example of music-color synesthesia operating as a production tool.