Although being relatively homogeneous within cetacean species, pigmentation patterns may greatly vary among conspecifics. It has been known for a few decades that some Delphinus delphis individuals may show an anomalous pigmentation: In the most frequent case, the yellow patch that produces the usual hourglass-like pattern on the flanks is missing, leading to a very dark appearance. Such individuals have been described from several areas around the globe (notably Eastern Pacific, North-Eastern Atlantic and South-Western Pacific oceans), but the phenomenon is difficult to quantify, which prevents comparison between areas. Here we study the occurrence of this abnormal dark pattern using at-sea visual data obtained by Groupe de Recherche sur les Cétacés with a 11-meter-long sailboat and a consistent methodology, that provided several hundreds of common dolphins visual sightings with or without anomalously pigmented animals. In order to be usable in this study, we considered that a sighting should have three properties: duration longer than 3 minutes, minimal distance between the dolphins and the boat shorter than 50 meters, good environmental conditions (daylight, sea state inferior to Beaufort 3). Once filtered, the dataset consists of 185 sightings obtained from 1992 to 2022 in four European areas: Mediterranean sea, Western Iberia, Azores and Bay of Biscay. Presence of dark pigmented common dolphins was noted in 15 sightings (0% (0/42) in the Mediterranean, 17% (2/12) in Western Iberia, 7% (6/83) in the Azores and 15% (7/48) in the Bay of Biscay). The geographical distribution of these individuals (relative homogeneity of the prevalence in the North-Eastern Atlantic, opposed to the absence of this pigmentation in the Mediterranean) might be sign of differential genetic flows between areas. These observations highlight the usefulness of consistent boat-based cetologic fieldwork. Paul Fischer had already described in 1881 a melanistic dolphin: could he have already observed this melanistic variant on the French coast of the Bay of Biscay and given it a specific name?