The fin whale is brownish to dark or light gray dorsally and white ventrally. The left side of the head is dark gray, while the right side exhibits a complex pattern of contrasting light and dark markings. On the right lower jaw is a white or light gray "right mandible patch", which sometimes extends out as a light "blaze" laterally and dorsally unto the upper jaw and back to just behind the blowholes. Two narrow dark stripes originate from the eye and ear, the former widening into a large dark area on the shoulder—these are separated by a light area called the "interstripe wash". These markings are more prominent on individuals in the North Atlantic than in the North Pacific, where they can appear indistinct. The left side exhibits similar but much fainter markings. Dark, oval-shaped areas of pigment called "flipper shadows" extend below and posterior to the pectoral fins. This type of asymmetry is seen in Omura's whale and occasionally in minke whales. It was thought to have evolved because the whale swims on its right side when surface lunging and it sometimes circles to the right while at the surface above a prey patch. However, the whales just as often circle to the left. No accepted hypothesis explains the asymmetry.