A total of 58 specimens of Trachinus draco Linnaeus, 1758 were caught in Galician waters (Northwest Spain) and the Gulf of Cádiz (South Spain) between June and November 2020. Twenty-eight of them were males. They showed a distinct dark patch located above the pectoral fin and below the lateral line on both sides of the body. Bibliographic and photographic data showed the same coloration pattern over time and throughout their range of distribution. A temporary nuptial coloration in males is proposed for the first time as the cause of this coloration.